Don't pass null to memcmp.

This will allow us to add nonnull-attribute to the UBSAN bot.

We are in fact hitting a case where one of the arguments is null and the other
not, which seems dicey.  I think the scenario is comparing the empty pathref
with another path ref that's just been COWed, without any verbs or points yet.

BUG=skia:

Review URL: https://codereview.chromium.org/732643002

1 files changed, 6 insertions, 0 deletions

diff --git a/src/core/SkPathRef.cpp b/src/core/SkPathRef.cpp
index dffb6a3646..ad85fd06a8 100644
--- a/src/core/SkPathRef.cpp
+++ b/src/core/SkPathRef.cpp
@@ -193,12 +193,18 @@ bool SkPathRef::operator== (const SkPathRef& ref) const {
         SkASSERT(!genIDMatch);
         return false;
     }
+    if (0 == ref.fVerbCnt) {
+        SkASSERT(0 == ref.fPointCnt);
+        return true;
+    }
+    SkASSERT(this->verbsMemBegin() && ref.verbsMemBegin());
     if (0 != memcmp(this->verbsMemBegin(),
                     ref.verbsMemBegin(),
                     ref.fVerbCnt * sizeof(uint8_t))) {
         SkASSERT(!genIDMatch);
         return false;
     }
+    SkASSERT(this->points() && ref.points());
     if (0 != memcmp(this->points(),
                     ref.points(),
                     ref.fPointCnt * sizeof(SkPoint))) {