Throw NullPointerException on args to Time#compare

Check for null on arguments to Time#compare(Time, Time) before passing
it down to JNI code.

Bug: 5073949
Change-Id: I077e9d5194a89206d1e51fc89a72c8a72e29f8f1
diff --git a/core/jni/android_text_format_Time.cpp b/core/jni/android_text_format_Time.cpp
index c152aa8..69c6021 100644
--- a/core/jni/android_text_format_Time.cpp
+++ b/core/jni/android_text_format_Time.cpp
@@ -641,7 +641,7 @@
     /* name, signature, funcPtr */
     { "normalize",               "(Z)J",                                        (void*)android_text_format_Time_normalize },
     { "switchTimezone",          "(Ljava/lang/String;)V",                       (void*)android_text_format_Time_switchTimezone },
-    { "compare",                 "(Landroid/text/format/Time;Landroid/text/format/Time;)I",     (void*)android_text_format_Time_compare },
+    { "nativeCompare",           "(Landroid/text/format/Time;Landroid/text/format/Time;)I",     (void*)android_text_format_Time_compare },
     { "format1",                 "(Ljava/lang/String;)Ljava/lang/String;",      (void*)android_text_format_Time_format },
     { "format2445",              "()Ljava/lang/String;",                        (void*)android_text_format_Time_format2445 },
     { "toString",                "()Ljava/lang/String;",                        (void*)android_text_format_Time_toString },