ObjC RTCEAGLVideoVideo: Check GL context is non-nil in constructor

RTCEAGLVideoVideo ensureGLContext has been observed to fail because the
GL context is nil. This CL checks the GL context is non-nil in the ctor
instead.

BUG=b/62865840

Review-Url: https://codereview.webrtc.org/2991863002
Cr-Commit-Position: refs/heads/master@{#19189}

webrtc/sdk/objc/Framework/Classes/UI/RTCEAGLVideoView.m

@@ -121,7 +121,9 @@
 - (instancetype)initWithFrame:(CGRect)frame shader:(id<RTCVideoViewShading>)shader {
   if (self = [super initWithFrame:frame]) {
     _shader = shader;
-    [self configure];
+    if (![self configure]) {
+      return nil;
+    }
   }
   return self;
 }
@@ -129,17 +131,23 @@
 - (instancetype)initWithCoder:(NSCoder *)aDecoder shader:(id<RTCVideoViewShading>)shader {
   if (self = [super initWithCoder:aDecoder]) {
     _shader = shader;
-    [self configure];
+    if (![self configure]) {
+      return nil;
+    }
   }
   return self;
 }
 
-- (void)configure {
+- (BOOL)configure {
   EAGLContext *glContext =
     [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES3];
   if (!glContext) {
     glContext = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];
   }
+  if (!glContext) {
+    RTCLogError(@"Failed to create EAGLContext");
+    return NO;
+  }
   _glContext = glContext;
 
   // GLKView manages a framebuffer for us.
@@ -176,6 +184,7 @@
       [strongSelf displayLinkTimerDidFire];
     }];
   [self setupGL];
+  return YES;
 }
 
 - (void)dealloc {