Common (Windows): allows COM be used in C sources

src/common/windows/com.c

@@ -1,4 +1,4 @@
-#include "com.hpp"
+#include "com.h"
 
 #include <roapi.h>
 

src/common/windows/com.h

@@ -1,23 +1,23 @@
 #pragma once
 
-#ifdef __cplusplus
-
-    #include "common/attributes.h"
-    #include <unknwn.h>
+#include "common/attributes.h"
+#include <assert.h>
+#include <unknwn.h>
 
 // Initialize COM & WinRT
 const char* ffInitCom(void);
 
 static inline void ffReleaseComObject(void* ppUnknown) {
+    assert(ppUnknown);
     IUnknown* pUnknown = *(IUnknown**) ppUnknown;
     if (pUnknown) {
+#ifdef __cplusplus
         pUnknown->Release();
+#else
+        pUnknown->lpVtbl->Release(pUnknown);
+#endif
+        *(IUnknown**) ppUnknown = NULL;
     }
 }
 
-    #define FF_AUTO_RELEASE_COM_OBJECT FF_A_CLEANUP(ffReleaseComObject)
-
-#else
-    // Win32 COM headers requires C++ compiler
-    #error Must be included in C++ source file
-#endif
+#define FF_AUTO_RELEASE_COM_OBJECT FF_A_CLEANUP(ffReleaseComObject)