TlsValidator: fix uninitialized member

Init default value of caValidationOutput_ member of TlsValidator class.
This prevents warns from static coverage tests.

(issue detected by coverity.com analysis)

Change-Id: Ib9a930bb233208cd99b7003d1a72b6d8003e3e9d
Tuleap: #909

src/security/tlsvalidator.h

@@ -282,7 +282,7 @@ private:
     bool privateKeyMatch_ {false};
 
     bool caChecked_ {false};
-    unsigned int caValidationOutput_;
+    unsigned int caValidationOutput_ {0}; // 0 means "no flags set", where flags are ones from gnutls_certificate_status_t
 
     mutable char copy_buffer[4096];