Fix bug https://github.com/aminroosta/sqlite_modern_cpp/issues/16

Replace current_exception with uncaught_exception as the former is
active in a catch block. This prevents running db queries in a catch block
as the library won't query when the stack is unwinding.

Author: Edward Rosten

hdr/sqlite_modern_cpp.h

@@ -203,7 +203,7 @@ class database_binder {
 
 		/* Will be executed if no >>op is found, but not if an exception
 		   is in mud flight */
-		if (!execution_started && !std::current_exception()) {
+		if (!execution_started && !std::uncaught_exception()) {
 			int hresult;
 
 			while ((hresult = sqlite3_step(_stmt)) == SQLITE_ROW) { }