[rcore] use LOG_WARNING when InitPlatform() fails

...as this is preferred over LOG_ERROR.

Requested-by: https://github.com/raysan5/raylib/pull/4803#discussion_r1976651724

src/rcore.c

@@ -685,7 +685,7 @@ void InitWindow(int width, int height, const char *title)
 
     if (result != 0)
     {
-        TRACELOG(LOG_ERROR, "SYSTEM: Failed to initialize Platform");
+        TRACELOG(LOG_WARNING, "SYSTEM: Failed to initialize Platform");
         return;
     }
     //--------------------------------------------------------------