Handle dwCreationDisposition in CreateFileA to fix PSYLINK (#60)

Before this change, dwCreationDisposition parameter of CreateFileA was
ignored by wibo. However, it turns out that PSYLINK.EXE in PsyQ 4.4
sometimes depends on correct handling of that parameter.

When building overlays with PSYLINK.EXE, it sometimes opens the
resulting overlay file the second time, with OPEN_EXISTING creation
disposition (as opposed to TRUNCATE_EXISTING). Before the change,
wibo opened that file with fopen(..., "wb+") which truncated the file
even though OPEN_EXISTING (non-truncating) was requested. This affected
https://github.com/foxdieteam/mgs_reversing, where one of the overlays
(camera.bin) was built incorrectly when using wibo (worked correctly
on Windows or with wine).

This commit adds proper handling of dwCreationDisposition parameter.
The file now can be opened in truncating or non-truncating mode.
Additionally, the implementation now reacts correctly to file
existing/non-existing as specified by the requested creation disposition
mode. For example, if CreateFileA is called with OPEN_EXISTING and the
file does not exist it will set an error and not create a new file
(the previous behavior). If the file exists, it's opened in
non-truncating mode, as TRUNCATE_EXISTING or CREATE_ALWAYS is required
for truncation.

After the fix you can correctly build the whole mgs_reversing project
with wibo - tools running under wibo: ASMPSX, ASPSX, CC1PSX 4.0 & 4.4,
PSYLINK. I have NOT tested other executables apart from those.

dll/kernel32.cpp

@@ -840,6 +840,13 @@ namespace kernel32 {
 		return 1;
 	}
 
+	enum {
+		CREATE_NEW = 1,
+		CREATE_ALWAYS = 2,
+		OPEN_EXISTING = 3,
+		OPEN_ALWAYS = 4,
+		TRUNCATE_EXISTING = 5,
+	};
 	void *WIN_FUNC CreateFileA(
 			const char* lpFileName,
 			unsigned int dwDesiredAccess,
@@ -853,19 +860,72 @@ namespace kernel32 {
 				lpFileName, path.c_str(),
 				dwDesiredAccess, dwShareMode, lpSecurityAttributes,
 				dwCreationDisposition, dwFlagsAndAttributes);
+
+		wibo::lastError = 0; // possibly overwritten later in this function
+
+		// Based on https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea#parameters
+		// and this table: https://stackoverflow.com/a/14469641
+		bool fileExists = (access(path.c_str(), F_OK) == 0);
+		bool shouldTruncate = false;
+		switch (dwCreationDisposition) {
+			case CREATE_ALWAYS:
+				if (fileExists) {
+					wibo::lastError = 183; // ERROR_ALREADY_EXISTS
+					shouldTruncate = true; // "The function overwrites the file"
+					// Function succeeds
+				}
+				break;
+			case CREATE_NEW:
+				if (fileExists) {
+					wibo::lastError = 80; // ERROR_FILE_EXISTS
+					return INVALID_HANDLE_VALUE;
+				}
+				break;
+			case OPEN_ALWAYS:
+				if (fileExists) {
+					wibo::lastError = 183; // ERROR_ALREADY_EXISTS
+					// Function succeeds
+				}
+				break;
+			case OPEN_EXISTING:
+				if (!fileExists) {
+					wibo::lastError = 2; // ERROR_FILE_NOT_FOUND
+					return INVALID_HANDLE_VALUE;
+				}
+				break;
+			case TRUNCATE_EXISTING:
+				shouldTruncate = true;
+				if (!fileExists) {
+					wibo::lastError = 2; // ERROR_FILE_NOT_FOUND
+					return INVALID_HANDLE_VALUE;
+				}
+				break;
+			default:
+				assert(0);
+		}
+
 		FILE *fp;
 		if (dwDesiredAccess == 0x80000000) { // read
 			fp = fopen(path.c_str(), "rb");
 		} else if (dwDesiredAccess == 0x40000000) { // write
-			fp = fopen(path.c_str(), "wb");
+			if (shouldTruncate || !fileExists) {
+				fp = fopen(path.c_str(), "wb");
+			} else {
+				// There is no way to fopen with only write permissions
+				// and without truncating the file...
+				fp = fopen(path.c_str(), "rb+");
+			}
 		} else if (dwDesiredAccess == 0xc0000000) { // read/write
-			fp = fopen(path.c_str(), "wb+");
+			if (shouldTruncate || !fileExists) {
+				fp = fopen(path.c_str(), "wb+");
+			} else {
+				fp = fopen(path.c_str(), "rb+");
+			}
 		} else {
 			assert(0);
 		}
 
 		if (fp) {
-			wibo::lastError = 0;
 			void *handle = files::allocFpHandle(fp);
 			DEBUG_LOG("-> %p\n", handle);
 			return handle;