fix fuzzes

src/pathops/SkOpCoincidence.cpp

Index: src/pathops/SkOpCoincidence.cpp
diff --git a/src/pathops/SkOpCoincidence.cpp b/src/pathops/SkOpCoincidence.cpp
index 5bae6f56b832a51d0a54f0385630b66399eed6b5..ea84e04e01e91b391c7f13d5ff94ae91b02fb30c 100755
--- a/src/pathops/SkOpCoincidence.cpp
+++ b/src/pathops/SkOpCoincidence.cpp
@@ -1364,6 +1364,9 @@ bool SkOpCoincidence::mark() {
         return true;
     }
     do {
+        if (!coin->coinPtTStartWritable()->span()->upCastable()) {
+            return false;
+        }
         SkOpSpan* start = coin->coinPtTStartWritable()->span()->upCast();
         SkASSERT(!start->deleted());
         SkOpSpanBase* end = coin->coinPtTEndWritable()->span();