[rtext] Don't return default font if LoadFontEx fails (#4077)

It is currently impossible to check a font loaded successfully with
IsFontReady because LoadFontEx will always return a valid font.

DrawTextEx has this check:
if (font.texture.id == 0) font = GetFontDefault();  // Security check in case of not valid font

So anyone relying on the default font as a fallback for fonts failing to
load should still be covered.

src/rtext.c

@@ -394,7 +394,6 @@ Font LoadFontEx(const char *fileName, int fontSize, int *codepoints, int codepoi
 
         UnloadFileData(fileData);
     }
-    else font = GetFontDefault();
 
     return font;
 }