Function `clang_Type_getObjCEncoding` causes segmentation fault if called with `Invalid` type

[YSakhno]

If the libclang function clang_Type_getObjCEncoding() is called with an invalid type (that is type whose kind is CXType_Invalid), it fails with a segmentation fault.

Expected behavior

The function should not fail for any input that can be legitimately obtained from other libclang functions. If the type is 'unsupported', an empty string can be returned (for example).