Fix a couple of asserts

Polarity was reversed.

Change-Id: I15af89267a703210ae5d08a9cca529b2f0cd48c6
diff --git a/vm/interp/Interp.c b/vm/interp/Interp.c
index 7ad3096..9df0d23 100644
--- a/vm/interp/Interp.c
+++ b/vm/interp/Interp.c
@@ -649,7 +649,7 @@
     if (self->interpBreak.ctl.subMode & kSubModeDebuggerActive) {
         Object* thisPtr = dvmGetThisPtr(self->interpSave.method,
                                         self->interpSave.fp);
-        assert(thisPtr != NULL && !dvmIsValidObject(thisPtr));
+        assert(thisPtr == NULL || dvmIsValidObject(thisPtr));
         dvmDbgPostLocationEvent(methodToCall, -1, thisPtr, DBG_METHOD_ENTRY);
     }
 }
@@ -664,7 +664,7 @@
     if (self->interpBreak.ctl.subMode & kSubModeDebuggerActive) {
         Object* thisPtr = dvmGetThisPtr(self->interpSave.method,
                                         self->interpSave.fp);
-        assert(thisPtr != NULL && !dvmIsValidObject(thisPtr));
+        assert(thisPtr == NULL || dvmIsValidObject(thisPtr));
         dvmDbgPostLocationEvent(methodToCall, -1, thisPtr, DBG_METHOD_EXIT);
     }
     if (self->interpBreak.ctl.subMode & kSubModeMethodTrace) {