Free potentially allocated regexes from Params::evalGrep

In Params::evalGrep regcomp allocates some internal space for the regex objects,
which must be freed manually via regfree(). This was however only done when the
call to regcomp() failed and not on success. As the regexes are needed later,
they have to be deallocated by the destructor.

src/exiv2.cpp

@@ -193,6 +193,14 @@ Params& Params::instance()
     return *instance_;
 }
 
+Params::~Params() {
+#if defined(EXV_HAVE_REGEX_H)
+    for (size_t i=0; i<instance().greps_.size(); ++i) {
+        regfree(&instance().greps_.at(i));
+    }
+#endif
+}
+
 void Params::cleanup()
 {
     delete instance_;

src/exiv2app.hpp

@@ -296,6 +296,9 @@ private:
     //! Prevent copy-construction: not implemented.
     Params(const Params& rhs);
 
+    //! Destructor, frees any allocated regexes in greps_
+    ~Params();
+
     //! @name Helpers
     //@{
     int setLogLevel(const std::string& optarg);