FuzzPath() should probably make a valid path

This will point out if something's gone screwy earlier in Debug builds.

Bug: oss-fuzz:10488

Change-Id: Ib091ada75344140bbe2932e5c2f1e2257f05019b
Reviewed-on: https://skia-review.googlesource.com/156660
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
diff --git a/fuzz/FuzzCommon.cpp b/fuzz/FuzzCommon.cpp
index 3236f1c..a6fd081 100644
--- a/fuzz/FuzzCommon.cpp
+++ b/fuzz/FuzzCommon.cpp
@@ -206,6 +206,8 @@
                 SkASSERT(false);
                 break;
         }
+        SkASSERT(path->isValid());
+        SkASSERT(path->pathRefIsValid());
     }
 }