"Fix" some ImageFilter fuzzer issues

SkClipOp.h & SkPictureFlat.h
   Invalid SkClipOps were getting through - the question here is where (for a class enum) is a good place to put the k*Mask definition.

SkPath1DPathEffect
   NaNs were getting past.

SkBlurMaskFilter
   Assert wasn't necessary since we whacked the flag on the next line.

Change-Id: I87f95ad39f4760284f881d7c4500eb82fcdba282
Reviewed-on: https://skia-review.googlesource.com/6194
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Herb Derby <herb@google.com>
diff --git a/tests/BlurTest.cpp b/tests/BlurTest.cpp
index 2893a0c..f2c35d7 100644
--- a/tests/BlurTest.cpp
+++ b/tests/BlurTest.cpp
@@ -507,7 +507,7 @@
     // Test asABlur for SkBlurMaskFilter
     //
     for (size_t i = 0; i < SK_ARRAY_COUNT(styles); ++i) {
-        const SkBlurStyle style = (SkBlurStyle)styles[i];
+        const SkBlurStyle style = styles[i];
         for (size_t j = 0; j < SK_ARRAY_COUNT(sigmas); ++j) {
             const SkScalar sigma = sigmas[j];
             for (int flags = 0; flags <= SkBlurMaskFilter::kAll_BlurFlag; ++flags) {