Initialized members of SnappyArrayWriter and SnappyDecompressionValidator.

These members were almost surely initialized before use by other member
functions, but Coverity was warning about this. Eliminating these warnings
minimizes clutter in that report and the likelihood of overlooking a real bug.

A=cmumford
R=jeff

snappy.cc

@@ -1147,7 +1147,8 @@ class SnappyArrayWriter {
  public:
   inline explicit SnappyArrayWriter(char* dst)
       : base_(dst),
-        op_(dst) {
+        op_(dst),
+        op_limit_(dst) {
   }
 
   inline void SetExpectedLength(size_t len) {
@@ -1254,7 +1255,7 @@ class SnappyDecompressionValidator {
   size_t produced_;
 
  public:
-  inline SnappyDecompressionValidator() : produced_(0) { }
+  inline SnappyDecompressionValidator() : expected_(0), produced_(0) { }
   inline void SetExpectedLength(size_t len) {
     expected_ = len;
   }