[fix] Allow default FM rotation on init when `Keep FM rotation` is disabled (#6348)

frontend/apps/filemanager/filemanager.lua

@@ -70,10 +70,12 @@ function FileManager:onSetRotationMode(rotation)
     return true
 end
 
-function FileManager:setRotationMode()
+-- init should be set to True when starting the FM for the first time
+-- (not coming from the reader). This allows the default to be properly set.
+function FileManager:setRotationMode(init)
     local locked = G_reader_settings:readSetting("lock_rotation")
-    local rotation_mode = G_reader_settings:readSetting("fm_rotation_mode") or 0
-    if locked then
+    local rotation_mode = G_reader_settings:readSetting("fm_rotation_mode") or Screen.ORIENTATION_PORTRAIT
+    if locked or init then
         self:onSetRotationMode(rotation_mode)
     end
 end

reader.lua

@@ -277,6 +277,7 @@ if ARGV[argidx] and ARGV[argidx] ~= "" then
         local home_dir =
             G_reader_settings:readSetting("home_dir") or ARGV[argidx]
         UIManager:nextTick(function()
+            FileManager:setRotationMode(true)
             FileManager:showFiles(home_dir)
         end)
         -- always open history on top of filemanager so closing history