SM: Fix FakeROM instances sharing the same data dictionary (#4912)

FakeROM instances were being created with default arguments, which
included a mutable default argument data dictionary, so all FakeROM
instances would be writing to and reading the same dictionary, resulting
in broken patch data in multiworlds with more than one Super Metroid
world.

worlds/sm/variaRandomizer/rom/rom.py

@@ -89,9 +89,12 @@ class ROM(object):
 
 class FakeROM(ROM):
     # to have the same code for real ROM and the webservice
-    def __init__(self, data={}):
+    def __init__(self, data=None):
         super(FakeROM, self).__init__()
-        self.data = data
+        if data is None:
+            self.data = {}
+        else:
+            self.data = data
         self.ipsPatches = []
 
     def write(self, bytes):