Ensure that mariadb_dr_do_error() always set error with all details

When DBIc_ERR is set to zero it indicates warning. So change zero error code to CR_UNKNOWN_ERROR.
Also ensure that DBIc_STATE is always set. Use "HY000" as fallback.

dbdimp.c

@@ -1345,17 +1345,22 @@ void mariadb_dr_do_error(SV* h, unsigned int rc, const char *what, const char *s
 
   if (DBIc_TRACE_LEVEL(imp_xxh) >= 2)
     PerlIO_printf(DBIc_LOGPIO(imp_xxh), "\t\t--> mariadb_dr_do_error\n");
+
+  if (!rc)
+    rc = CR_UNKNOWN_ERROR;
+  if (!what || !what[0])
+    what = "Unknown error";
+  if (!sqlstate || !sqlstate[0])
+    sqlstate = "HY000";
+
   errstr= DBIc_ERRSTR(imp_xxh);
   sv_setuv(DBIc_ERR(imp_xxh), rc);	/* set err early	*/
   SvUTF8_off(errstr);
   sv_setpv(errstr, what);
   sv_utf8_decode(errstr);
 
-  if (sqlstate)
-  {
     errstate= DBIc_STATE(imp_xxh);
     sv_setpv(errstate, sqlstate);
-  }
 
   /* NO EFFECT DBIh_EVENT2(h, ERROR_event, DBIc_ERR(imp_xxh), errstr); */
   if (DBIc_TRACE_LEVEL(imp_xxh) >= 2)