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>
4f294b3ab5