cmd/ebitenmobile: Bug fix: iOS view was not shown

This enbugs that garbages are rendered outside the screen. I think
the bug in iPad is now exposed to any iOS devices.

Updates #1019

cmd/ebitenmobile/gobind.go

@@ -216,6 +216,15 @@ const objcM = `// Code generated by ebitenmobile. DO NOT EDIT.
   [displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
 }
 
+- (void)viewWillLayoutSubviews {
+  CGRect viewRect = [[self view] frame];
+#if EBITEN_METAL
+  [[self metalView] setFrame:viewRect];
+#else
+  [[self glkView] setFrame:viewRect];
+#endif
+}
+
 - (void)viewDidLayoutSubviews {
   [super viewDidLayoutSubviews];
   CGRect viewRect = [[self view] frame];