Filter out empty string CLSIDs.

There's more detail in the comment, but this fixes an issue where some
Mosquito loadouts could not be loaded.

Might fix https://github.com/dcs-liberation/dcs_liberation/issues/3171.
There aren't enough instructions in the bug for me to be sure, but it
sounds like a similar problem, although I came across it with bombs
rather than rockets.

game/ato/loadouts.py

@@ -134,7 +134,17 @@ class Loadout:
             pylons = payload["pylons"]
             try:
                 pylon_assignments = {
-                    p["num"]: Weapon.with_clsid(p["CLSID"]) for p in pylons.values()
+                    p["num"]: Weapon.with_clsid(p["CLSID"])
+                    for p in pylons.values()
+                    # When unloading incompatible pylons (for example, some of the
+                    # Mosquito's pylons cannot be loaded when other pylons are carrying
+                    # rockets), DCS sometimes equips the empty string rather than
+                    # unsetting the pylon. An unset pylon and the empty string appear to
+                    # have identical behavior, and it's annoying to deal with weapons
+                    # that pydcs doesn't know about, so just clear those pylons rather
+                    # than explicitly handling "".
+                    # https://github.com/dcs-liberation/dcs_liberation/issues/3171
+                    if p["CLSID"] != ""
                 }
             except KeyError:
                 logging.exception(