layers: Fix VerifyCopyUpdateContents on combined image sampler descriptors

A missing break at the end of the ImageSampler case results in falling
through to the Image case, leading to spurious validation errors such as:

  vkUpdateDescriptorsSets() failed copy update from Descriptor Set 0x108
  to Descriptor Set 0x137 with error: Attempted copy update to image
  descriptor failed due to: Invalid VkImageView: 0x100000000
diff --git a/layers/descriptor_sets.cpp b/layers/descriptor_sets.cpp
index d7ca025..d08a110 100644
--- a/layers/descriptor_sets.cpp
+++ b/layers/descriptor_sets.cpp
@@ -1359,6 +1359,7 @@
                 return false;
             }
         }
+        break;
     }
     case Image: {
         for (uint32_t di = 0; di < update->descriptorCount; ++di) {