Move FBO check from applyRenderTarget to the API.

We would traverse the applyRenderTarget path from several entry
points, which could then trigger a GL error. In-line with our
validation refactoring, move all error checks prior to executing
any state logic.

BUG=angle:571

Change-Id: I51f5bcfa41be7cdba7771eb87d5a831fa622f984
Reviewed-on: https://chromium-review.googlesource.com/203772
Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
diff --git a/src/libGLESv2/validationES.cpp b/src/libGLESv2/validationES.cpp
index 48520d5..ddb03fa 100644
--- a/src/libGLESv2/validationES.cpp
+++ b/src/libGLESv2/validationES.cpp
@@ -1340,6 +1340,12 @@
         return gl::error(GL_INVALID_OPERATION, false);
     }
 
+    const gl::Framebuffer *fbo = context->getDrawFramebuffer();
+    if (!fbo || fbo->completeness() != GL_FRAMEBUFFER_COMPLETE)
+    {
+        return gl::error(GL_INVALID_FRAMEBUFFER_OPERATION, false);
+    }
+
     // No-op if zero count
     return (count > 0);
 }