Tweak terminate() slightly

* Gave it a default argument, since we never actually care about it, but
it needs to have it to conform to the signal handler prototype
* Constricted the area locked by activeCrit to only the block that deals
with the connections vector, to lower the chance of a future badly
placed call to terminate() deadlocking the server instead

src/CNStructs.hpp

@@ -41,7 +41,7 @@ std::string U16toU8(char16_t* src);
 size_t U8toU16(std::string src, char16_t* des, size_t max); // returns number of char16_t that was written at des
 time_t getTime();
 time_t getTimestamp();
-void terminate(int);
+void terminate(int unused=0);
 
 // The PROTOCOL_VERSION definition is defined by the build system.
 #if !defined(PROTOCOL_VERSION)