PR libgcj/28178:
	* jni.cc (_Jv_JNI_DeleteLocalRef): Ignore null argument.
	(_Jv_JNI_DeleteGlobalRef): Likewise.
	* testsuite/libjava.jni/PR28178.java: New file.
	* testsuite/libjava.jni/PR28178.c: New file.
	* testsuite/libjava.jni/PR28178.out: New file.

From-SVN: r115034