[rcore] fix crash in InitWindow, due to unchecked result of InitPlatform (#4803)

* [rcore] fix crash in InitWindow, due to unchecked result of InitPlatform

Check the result of InitPlatform(), if it isn't 0, report the Error
and return. This prevent crashes and allows for gracefully aborting
or recovering by checking IsWindowReady().

Partially-fixes: https://github.com/raysan5/raylib/issues/4801

* [rcore] style: store the result of InitPlatform() before checking it

Small style change that doesn't impact how the code behaves here.
Variable 'result' is not used anywhere else in this block,
it's just for compliance with Raylib's coding conventions.

Requested in PR: https://github.com/raysan5/raylib/pull/4803#discussion_r1976502788

* [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

@@ -681,7 +681,13 @@ void InitWindow(int width, int height, const char *title)
 
     // Initialize platform
     //--------------------------------------------------------------
-    InitPlatform();
+    int result = InitPlatform();
+
+    if (result != 0)
+    {
+        TRACELOG(LOG_WARNING, "SYSTEM: Failed to initialize Platform");
+        return;
+    }
     //--------------------------------------------------------------
 
     // Initialize rlgl default data (buffers and shaders)