fix various problems, thanks CppCheck :) (#1005)

* explained a bit more the core_window_letterbox example

* fixed a few 'ups' moments that could lead to mild head pain and time loss

src/text.c

@@ -1394,7 +1394,7 @@ char *TextToUtf8(int *codepoints, int length)
     }
     
     // Resize memory to text length + string NULL terminator
-    realloc(text, size + 1);
+    text = realloc(text, size + 1);
     
     return text;
 }