regex filter: fix assertion fail if regex wasn't properly compiled

src/regex_filter.h

@@ -35,7 +35,7 @@ template <typename T> struct RegexFilter
 	bool operator()(const Item &item) {
 		if (m_rx.regex().empty())
 			return true;
-		if (!m_rx.error().empty())
+		if (!m_rx.compiled() || !m_rx.error().empty())
 			return false;
 		return m_filter(m_rx, item.value());
 	}

src/regexes.cpp

@@ -52,6 +52,11 @@ const std::string &Regex::error() const
 	return m_error;
 }
 
+bool Regex::compiled() const
+{
+	return m_compiled;
+}
+
 bool Regex::compile()
 {
 	if (m_compiled)

src/regexes.h

@@ -37,6 +37,9 @@ struct Regex
 	/// @return compilation error (if there was any)
 	const std::string &error() const;
 	
+	/// @return true if regular expression is compiled, false otherwise
+	bool compiled() const;
+	
 	/// compiles regular expression
 	/// @result true if compilation was successful, false otherwise
 	bool compile();