string_load: fix NoneType exceptions (no data at addr)

string_load.py

@@ -83,11 +83,15 @@ def check_string(start, length):
     end = start.add(length-1)
     if not range_printable(start, end):
         return False
+    datatype_name = 'None'
     data = listing.getDataAt(start)
-    datatype = data.getDataType().getName()
-    if datatype != 'string':
+    if data is not None:
+        datatype = data.getDataType()
+        if datatype is not None:
+            datatype_name = datatype.getName()
+    if datatype_name != 'string':
         newStr = makeString(start, length, end)
-        print("Found string not seen before (was %s) at %s of len %s: %s" % (datatype, start, length, newStr))
+        print("Found string not seen before (was %s) at %s of len %s: %s" % (datatype_name, start, length, newStr))
         return True
     data_len = data.getLength()
     if data_len > length: