Handle postgresql and sqlite3 libs properly

Do not fail to compile when one of them is missing but the other one is not.

Raise an error when trying to open a database with the missing library.

see #3237

src/main.cpp

@@ -6,8 +6,6 @@
 #include <utils/xdg.hpp>
 #include <utils/reload.hpp>
 
-#include <libpq-fe.h>
-
 #ifdef UDNS_FOUND
 # include <network/dns_handler.hpp>
 #endif
@@ -90,7 +88,8 @@ int main(int ac, char** av)
 #ifdef USE_DATABASE
   try {
     open_database();
-  } catch (...) {
+  } catch (const std::exception& e) {
+    log_error(e.what());
     return 1;
   }
 #endif