Explicitly try the default configuration

Up to now we assumed that the default config is in a path where
xdgConfigFind() finds it. However, evidently this is not always the
case, so make this explicitly try the default configuration file.

Fixes: https://github.com/awesomeWM/awesome/issues/1346
Signed-off-by: Uli Schlachter <psychon@znc.in>

config.h

@@ -4,6 +4,7 @@
 #define AWESOME_LUA_LIB_PATH  "@AWESOME_LUA_LIB_PATH@"
 #define XDG_CONFIG_DIR        "@XDG_CONFIG_DIR@"
 #define AWESOME_IS_BIG_ENDIAN @AWESOME_IS_BIG_ENDIAN@
+#define AWESOME_DEFAULT_CONF  "@AWESOME_SYSCONFDIR@/rc.lua"
 
 #cmakedefine WITH_DBUS
 #cmakedefine HAS_EXECINFO

luaa.c

@@ -885,8 +885,13 @@ luaA_find_config(xdgHandle* xdg, const char *confpatharg, luaA_config_callback *
         }
         tmp += a_strlen(tmp) + 1;
     }
-
     p_delete(&confpath);
+
+    if(callback(AWESOME_DEFAULT_CONF))
+    {
+        return a_strdup(AWESOME_DEFAULT_CONF);
+    }
+
     return NULL;
 }