CCEffects - Fix assertion failures when texture + normal map are missing

Under certain circumstances, the effect renderer could allocate a render target
with 0 x 0 dimensions which resulted in a GL error and assertion failure. Those
circumstances were:

- Sprite has no texture
- Sprite has no normal map
- An unstitchable effect stack is attached to the sprite

This is now fixed in the following ways:

- The effect renderer's render target dimensions now come from sprite.contentSize
not just sprite.texture.contentSize. This means that if the sprite has a normal map but
not a texture, the resulting size will come from the normal map instead of being 0 x 0 as
it was before.

- If the computed render target size is still 0 x 0, it is bumped to 1 x 1.

- An assertion on 0 x 0 dimensions is added to the render target allocation code
so this sort of error is caught higher up in the stack in the future.

Author: Thayer J Andrews

cocos2d/CCEffectNode.m

@@ -168,7 +168,7 @@ -(void)draw:(CCRenderer *)renderer transform:(const GLKMatrix4 *)transform
 
     if (_effect)
     {
-        _effectRenderer.contentSize = self.texture.contentSize;
+        _effectRenderer.contentSize = self.contentSize;
         if ([_effect prepareForRendering] == CCEffectPrepareSuccess)
         {
             // Preparing an effect for rendering can modify its uniforms

cocos2d/CCEffectRenderer.m

@@ -191,6 +191,9 @@ -(void)drawSprite:(CCSprite *)sprite withEffect:(CCEffect *)effect uniforms:(NSM
             renderPass.transform = GLKMatrix4MakeOrtho(0.0f, _contentSize.width, 0.0f, _contentSize.height, -1024.0f, 1024.0f);
 
             CGSize rtSize = CGSizeMake(_contentSize.width * _contentScale, _contentSize.height * _contentScale);
+            rtSize.width = (rtSize.width <= 1.0f) ? 1.0f : rtSize.width;
+            rtSize.height = (rtSize.height <= 1.0f) ? 1.0f : rtSize.height;
+            
             rt = [self renderTargetWithSize:rtSize];
 
             [renderPass begin:previousPassTexture];
@@ -249,6 +252,8 @@ - (void)restoreRenderTargetWithRenderer:(CCRenderer *)renderer
 
 - (CCEffectRenderTarget *)renderTargetWithSize:(CGSize)size
 {
+    NSAssert((size.width > 0.0f) && (size.height > 0.0f), @"Render targets must have non-zero dimensions.");
+
     // If there is a free render target available for use, return that one. If
     // not, create a new one and return that.
     CCEffectRenderTarget *rt = nil;

cocos2d/CCSprite.m

@@ -369,7 +369,7 @@ -(void)draw:(CCRenderer *)renderer transform:(const GLKMatrix4 *)transform;
 
 	if (_effect)
 	{
-		_effectRenderer.contentSize = self.texture.contentSize;
+		_effectRenderer.contentSize = self.contentSize;
 		if ([self.effect prepareForRendering] == CCEffectPrepareSuccess)
 		{
 			// Preparing an effect for rendering can modify its uniforms