Fix clang warnings

src/script.h

@@ -434,7 +434,7 @@ public:
         // Immediate operand
         if (opcode <= OP_PUSHDATA4)
         {
-            unsigned int nSize;
+            unsigned int nSize = 0;
             if (opcode < OP_PUSHDATA1)
             {
                 nSize = opcode;
@@ -646,7 +646,7 @@ public:
 
     template<typename Stream>
     void Unserialize(Stream &s, int nType, int nVersion) {
-        unsigned int nSize;
+        unsigned int nSize = 0;
         s >> VARINT(nSize);
         if (nSize < nSpecialScripts) {
             std::vector<unsigned char> vch(GetSpecialSize(nSize), 0x00);