Add guards for edge cases.

src/core/SkLinearBitmapPipeline.cpp

Index: src/core/SkLinearBitmapPipeline.cpp
diff --git a/src/core/SkLinearBitmapPipeline.cpp b/src/core/SkLinearBitmapPipeline.cpp
index 415179a0b1683e4ac612bdb3be17bbcb656b6977..221f74d30df84467b3018e06d2d9160a553ba84b 100644
--- a/src/core/SkLinearBitmapPipeline.cpp
+++ b/src/core/SkLinearBitmapPipeline.cpp
@@ -584,11 +584,13 @@ public:
 
     void pointSpan(Span span) override {
         SkASSERT(fDest + span.count() <= fEnd);
-        int32_t x = (int32_t)span.startX();
-        int32_t y = (int32_t)span.startY();
-        const uint32_t* src = this->pixelAddress(x, y);
-        memmove(fDest, src, span.count() * sizeof(uint32_t));
-        fDest += span.count();
+        if (span.length() != 0.0f) {
+            int32_t x = (int32_t)span.startX();

[Brian Osman, 2016/04/25 20:00:18]

Should these be using SkScalarFloorToInt, just to be more explicit about the
conversion that's happening?

[herb_g, 2016/04/25 20:36:36]

At this point, I know that startX > 0, so I want the much faster truncate
behavior. Changed to SkScalarTruncToInt, which I didn't know existed. Thanks.

+            int32_t y = (int32_t)span.startY();
+            const uint32_t* src = this->pixelAddress(x, y);
+            memmove(fDest, src, span.count() * sizeof(uint32_t));
+            fDest += span.count();
+        }
     }
 
     void repeatSpan(Span span, int32_t repeatCount) override {