When clearing dive file data, forget the saved git sha

Otherwise parse_file() thinks that this data has already been loaded and
doesn't re-read it, even though our internal data structures have been
erased - so a subsequent parse_file after clear_dive_file_data() that
opens the same git repository finishes successfully, but leaves the
dive_table empty which is of course incorrect.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

subsurface-core/divelist.c

@@ -44,6 +44,7 @@
 #include "display.h"
 #include "planner.h"
 #include "qthelperfromc.h"
+#include "git-access.h"
 
 static short dive_list_changed = false;
 
@@ -1159,4 +1160,5 @@ void clear_dive_file_data()
 	existing_filename = NULL;
 
 	reset_min_datafile_version();
+	saved_git_id = "";
 }