filetree.c add checks for invalid file entries

Admittedly I can not really think of a reason this would occur
in normal use but if it does it'll result in a crash so
better safe than sorry

Change-Id: I593652bb658475bbd9a18026243c02524f5e7ccb
diff --git a/apps/filetree.c b/apps/filetree.c
index 2570b46..e45348d 100644
--- a/apps/filetree.c
+++ b/apps/filetree.c
@@ -436,6 +436,12 @@
     int rc = GO_TO_PREVIOUS;
     char buf[MAX_PATH];
     struct entry* file = tree_get_entry_at(c, c->selected_item);
+    if (!file)
+    {
+        splashf(HZ, str(LANG_READ_FAILED), str(LANG_UNKNOWN));
+        return rc;
+    }
+
     int file_attr = file->attr;
     int len;
 
@@ -680,6 +686,12 @@
                 }
 
                 struct entry* file = tree_get_entry_at(c, c->selected_item);
+                if (!file)
+                {
+                    splashf(HZ, str(LANG_READ_FAILED), str(LANG_UNKNOWN));
+                    return rc;
+                }
+
                 plugin = filetype_get_plugin(file);
                 if (plugin)
                 {