TOOLS/autocrop.lua: switch to auto-copy hwdec during cropdetect

I didn't set file-local-options/hwdec because you have to store the
hwdec value to restore it after cropdetect anyway, and if the user
manually changes hwdec after cropdetect, the new value isn't reset when
changing file.

TOOLS/lua/autocrop.lua

@@ -85,6 +85,8 @@ timers = {
     detect_crop = nil
 }
 
+local hwdec_backup
+
 local command_prefix = options.suppress_osd and 'no-osd' or ''
 
 function is_filter_present(label)
@@ -128,6 +130,13 @@ function remove_filter(label)
     return false
 end
 
+function restore_hwdec()
+    if hwdec_backup then
+        mp.set_property("hwdec", hwdec_backup)
+        hwdec_backup = nil
+    end
+end
+
 function cleanup()
 
     -- Remove existing filter.
@@ -140,6 +149,8 @@ function cleanup()
             timers[index] = nil
         end
     end
+
+    restore_hwdec()
 end
 
 function detect_crop()
@@ -149,6 +160,13 @@ function detect_crop()
         return
     end
 
+    local hwdec_current = mp.get_property("hwdec-current")
+    if hwdec_current:find("-copy$") == nil and hwdec_current ~= "no" and
+       hwdec_current ~= "crystalhd" and hwdec_current ~= "rkmpp" then
+        hwdec_backup = mp.get_property("hwdec")
+        mp.set_property("hwdec", "auto-copy-safe")
+    end
+
     -- Insert the cropdetect filter.
     local limit = options.detect_limit
     local round = options.detect_round
@@ -181,6 +199,8 @@ function detect_end()
         timers.detect_crop = nil
     end
 
+    restore_hwdec()
+
     local meta = {}
 
     -- Verify the existence of metadata.