IECoreMaya::ImageFile : Fix with RGB images

Definitely looks like the 3 component color case is completely broken - ideally, I would test for this, but since it's currently broken and no one cares, I'm just making sure it compiles with -Wextra

Author: danieldresser

src/IECoreMaya/ImageFile.cpp

@@ -290,8 +290,10 @@ MStatus ImageFile::glLoad( const MImageFileInfo& info, unsigned int idx )
 	{
 		case 3:
 			glTexImage2D( GL_TEXTURE_2D, 0, GL_RGB, m_width, m_height, 0, GL_RGB, GL_FLOAT, &pixels[0] );
+			break;
 		case 4:
 			glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA, m_width, m_height, 0, GL_RGBA, GL_FLOAT, &pixels[0] );
+			break;
 		default:
 			assert(false);
 	}