fix fuzz

src/pathops/SkOpSegment.cpp

Index: src/pathops/SkOpSegment.cpp
diff --git a/src/pathops/SkOpSegment.cpp b/src/pathops/SkOpSegment.cpp
index 3fc21f4490ef142942db31b8dc663fa917517595..0e4eb64141c5ee8d9abe5e2c63db4fc4805cbd3e 100644
--- a/src/pathops/SkOpSegment.cpp
+++ b/src/pathops/SkOpSegment.cpp
@@ -331,7 +331,9 @@ SkOpPtT* SkOpSegment::addT(double t, AliasMatch allowAlias, bool* allocated) {
             }
             return span->ptT();
         }
-        SkASSERT(span != &fTail);
+        if (span == &fTail) {
+            return nullptr;
+        }
     } while ((span = span->upCast()->next()));
     SkASSERT(0);
     return nullptr;