layers: Fix VkBool32 return in vk-layer-generate.py.

This regressed in f4542e618, but is only visible when defining
VK_USE_PLATFORM_WIN32_KHR, so might have been missed. Fixes a
warning in MS 2015, as well as an incorrect return value.
diff --git a/vk-layer-generate.py b/vk-layer-generate.py
index a76c29a..4e39c56 100755
--- a/vk-layer-generate.py
+++ b/vk-layer-generate.py
@@ -1263,6 +1263,8 @@
                 using_line += '    if (skipCall)\n'
                 if proto.ret == "bool":
                     using_line += '        return false;\n'
+                elif proto.ret == "VkBool32":
+                    using_line += '        return VK_FALSE;\n'
                 elif proto.ret != "void":
                     using_line += '        return VK_ERROR_VALIDATION_FAILED_EXT;\n'
                 else: