Fix a few "Uninitialized scalar field" warnings

Fix a few warnings reported by Coverity.
None of these is critical, but making sure that class fields are
initialized can avoid heisenbugs.

src/wallet.h

@@ -905,6 +905,7 @@ public:
         strOtherAccount.clear();
         strComment.clear();
         nOrderPos = -1;
+        nEntryNo = 0;
     }
 
     IMPLEMENT_SERIALIZE