CAudioMacro: Make constructor explicit

Prevents implicit error-prone constructions from occurring.

src/Core/Resource/CAudioMacro.h

@@ -12,7 +12,7 @@ class CAudioMacro : public CResource
     std::vector<CAssetID> mSamples;
 
 public:
-    CAudioMacro(CResourceEntry *pEntry = 0)
+    explicit CAudioMacro(CResourceEntry *pEntry = nullptr)
         : CResource(pEntry)
     {}