Fix a crash if calling GetProcAddress for GetProcAddress (what?!)

* Would also happen for LoadLibrary variants, but the crashdump I got
  was for GetProcAddress.

renderdoc/os/win32/win32_hook.cpp

@@ -493,7 +493,7 @@ FARPROC WINAPI Hooked_GetProcAddress(HMODULE mod, LPCSTR func)
         if(found->origptr && *found->origptr == NULL)
           *found->origptr = (void *)GetProcAddress(mod, func);
 
-        if(*found->origptr == NULL)
+        if(found->origptr && *found->origptr == NULL)
           return NULL;
 
         return (FARPROC)found->hookptr;