fix: check for existence of the DB itself

The plugins don't export the prices cache anymore, so that's a bad thing
to check for to determine if the DB needs to be built.

Do the smart thing and check for the existence of the actual DB file
itself.

tradedangerous/plugins/eddblink_plug.py

@@ -355,7 +355,7 @@ def run(self):
 
         # We can probably safely assume that the plugin has never been run if
         # the prices file doesn't exist, since the plugin always generates it.
-        if not (self.tdb.dataPath / Path("TradeDangerous.prices")).exists():
+        if not (self.tdb.dataPath / Path("TradeDangerous.db")).exists():
             self.options["clean"] = True
 
         if self.getOption("clean"):

tradedangerous/plugins/spansh_plug.py

@@ -208,7 +208,7 @@ def __init__(self, *args, **kwargs):
         assert not (self.url and self.file), 'Provide either url or file, not both'
         if self.file and (self.file != '-'):
             self.file = (Path(self.tdenv.cwDir, self.file)).resolve()
-        if not Path(self.tdb.dataPath, "TradeDangerous.prices").exists():
+        if not Path(self.tdb.dataPath, "TradeDangerous.db").exists():
             ri_path = Path(self.tdb.dataPath, "RareItem.csv")
             rib_path = ri_path.with_suffix(".tmp")
             if ri_path.exists():