Fix uninitialized variable added in 5c55bf5

After discussing with BlueMatt, this appears to be harmless in its
current state since it's always set before it's used. Initialize it
anyway for readability and future safety.

Rebased-By: Wladimir J. van der Laan <laanwj@gmail.com>
Rebased-From: 106f133de6

src/main.h

@@ -1883,7 +1883,7 @@ private:
     int nDoS;
     bool corruptionPossible;
 public:
-    CValidationState() : mode(MODE_VALID), nDoS(0) {}
+    CValidationState() : mode(MODE_VALID), nDoS(0), corruptionPossible(false) {}
     bool DoS(int level, bool ret = false, bool corruptionIn = false) {
         if (mode == MODE_ERROR)
             return ret;