SkStream Testing: fix bug in new unit test.

tests/StreamTest.cpp

Index: tests/StreamTest.cpp
diff --git a/tests/StreamTest.cpp b/tests/StreamTest.cpp
index 08adf142c10313bb0f1b4983556db9ec025387a4..6f78eca5f0de6c4554db514ccad9c0fbb9138e38 100644
--- a/tests/StreamTest.cpp
+++ b/tests/StreamTest.cpp
@@ -343,15 +343,15 @@ public:
     DumbStream(const uint8_t* data, size_t n)
         : fData(data), fCount(n), fIdx(0) {}
     size_t read(void* buffer, size_t size) override {
-        size_t c = SkTMin(fCount - fIdx, size);
-        if (c) {
-            memcpy(buffer, &fData[fIdx], size);
-            fIdx += c;
+        size_t copyCount = SkTMin(fCount - fIdx, size);
+        if (copyCount) {
+            memcpy(buffer, &fData[fIdx], copyCount);
+            fIdx += copyCount;
         }
-        return c;
+        return copyCount;
     }
     bool isAtEnd() const override {
-        return fCount > fIdx;
+        return fCount == fIdx;
     }
  private:
     const uint8_t* fData;