[gnome-shell/cherry-pick-46547ae0] shell-mime-sniffer: Ignore invalid file content type

[Marco Trevisan <marcotrevi src gnome org>]

commit ff73f76527303937ddd456ac925f44c5847e6980
Author: Marco Trevisan (Treviño) <mail 3v1n0 net>
Date:   Fri Jun 5 14:12:58 2020 +0000

    shell-mime-sniffer: Ignore invalid file content type
    
    The shell mime sniffer goes through all the files in a directory,
    however in case a file content type is not recognized, the GIO function
    g_file_info_get_content_type() may return NULL, causing a crash when
    looking up into the content type tables, as they are supposed to contain
    strings only and they use `g_str_hash` has func, which doesn't support
    NULL values.
    
    So, in case we get an invalid content type, let's just ignore it,
    without adding it to the cache as we do in the nautilus code that was
    inspiring the sniffer.
    
    Fixes https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/2643
    
    
    (cherry picked from commit 46547ae02797558699510595b27857b80c027b5b)

 src/hotplug-sniffer/shell-mime-sniffer.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/src/hotplug-sniffer/shell-mime-sniffer.c b/src/hotplug-sniffer/shell-mime-sniffer.c
index 6c56ecbaf5..7a1c1fe895 100644
--- a/src/hotplug-sniffer/shell-mime-sniffer.c
+++ b/src/hotplug-sniffer/shell-mime-sniffer.c
@@ -253,7 +253,9 @@ deep_count_one (DeepCountState *state,
   else
     {
       content_type = g_file_info_get_content_type (info);
-      add_content_type_to_cache (state, content_type);
+
+      if (content_type)
+        add_content_type_to_cache (state, content_type);
     }
 }