app: resolve build warnings

iOS builders fail to build the mobile repository because of compile
warnings.

1. "go build golang.org/x/mobile/app" can result in build error because
   of the warning "missing [super prepareOpenGL] call".

2. "null passed to a callee that requires a non-null argument" because
   argv is expected to not be a null argument.

Resolve these warnings.

Change-Id: I86130abc3a104be388475f5c316f5c3aef13aa92
Reviewed-on: https://go-review.googlesource.com/c/mobile/+/387094
Reviewed-by: Hajime Hoshi <hajimehoshi@gmail.com>
Trust: Hajime Hoshi <hajimehoshi@gmail.com>
Run-TryBot: Changkun Ou <mail@changkun.de>
TryBot-Result: Gopher Robot <gobot@golang.org>
Trust: Hyang-Ah Hana Kim <hyangah@gmail.com>
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>

Author: changkun

app/darwin_desktop.m

@@ -34,6 +34,7 @@ @interface MobileGLView : NSOpenGLView<NSApplicationDelegate, NSWindowDelegate>
 
 @implementation MobileGLView
 - (void)prepareOpenGL {
+	[super prepareOpenGL];
 	[self setWantsBestResolutionOpenGLSurface:YES];
 	GLint swapInt = 1;
 

app/darwin_ios.m

@@ -136,8 +136,9 @@ - (void)touchesCanceled:(NSSet*)touches withEvent:(UIEvent*)event {
 @end
 
 void runApp(void) {
+	char* argv[] = {};
 	@autoreleasepool {
-		UIApplicationMain(0, nil, nil, NSStringFromClass([GoAppAppDelegate class]));
+		UIApplicationMain(0, argv, nil, NSStringFromClass([GoAppAppDelegate class]));
 	}
 }