fixes mcedit not running without a file parameter

https://bugs.gentoo.org/show_bug.cgi?id=409107
https://www.midnight-commander.org/ticket/2754
https://www.midnight-commander.org/changeset/529a7ba24c9da9fdb1df939ff0fe35c6d27e65df

--- src/filemanager/ext.c
+++ src/filemanager/ext.c
@@ -637,4 +637,7 @@
     int have_type = 0;          /* Flag used by regex_check_type() */
 
+    if (filename_vpath == NULL)
+        return 0;
+
     /* Check for the special View:%d parameter */
     if (strncmp (action, "View:", 5) == 0)
--- src/filemanager/midnight.c
+++ src/filemanager/midnight.c
@@ -952,9 +952,11 @@
     case MC_RUN_EDITOR:
         {
-            vfs_path_t *param_vpath;
-
-            param_vpath = vfs_path_from_str (mc_run_param0);
-            ret = edit_file (param_vpath, mc_args__edit_start_line);
-            vfs_path_free (param_vpath);
+            vfs_path_t *vpath = NULL;
+
+            if (mc_run_param0 != NULL && *mc_run_param0 != '\0')
+                vpath = vfs_path_from_str (mc_run_param0);
+
+            ret = edit_file (vpath, mc_args__edit_start_line);
+            vfs_path_free (vpath);
         }
         break;
@@ -962,7 +964,9 @@
     case MC_RUN_VIEWER:
         {
-            vfs_path_t *vpath;
-
-            vpath = prepend_cwd_on_local (mc_run_param0);
+            vfs_path_t *vpath = NULL;
+
+            if (mc_run_param0 != NULL && *mc_run_param0 != '\0')
+                vpath = prepend_cwd_on_local (mc_run_param0);
+
             view_file (vpath, 0, 1);
             vfs_path_free (vpath);