[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

src/rcore.c

@@ -681,7 +681,10 @@ void InitWindow(int width, int height, const char *title)
 
     // Initialize platform
     //--------------------------------------------------------------
-    if(InitPlatform() != 0) {
+    int result = InitPlatform();
+
+    if (result != 0)
+    {
         TRACELOG(LOG_ERROR, "SYSTEM: Failed to initialize Platform");
         return;
     }