Make StringyInteger and StringyFloat return None when they can't parse the…

Make StringyInteger and StringyFloat return None when they can't parse the string from json, and don't try to overwrite max_attempts if it's ''

common/lib/xmodule/xmodule/capa_module.py

@@ -32,7 +32,7 @@ class StringyInteger(Integer):
         try:
             return int(value)
         except:
-            return value
+            return None
 
 
 class StringyFloat(Float):
@@ -43,7 +43,7 @@ class StringyFloat(Float):
         try:
             return float(value)
         except:
-            return value
+            return None
 
 
 # Generated this many different variants of problems with rerandomize=per_student
@@ -140,9 +140,6 @@ class CapaModule(CapaFields, XModule):
                 # see comment on randomization_bin
                 self.seed = randomization_bin(system.seed, self.location.url)
 
-        if self.max_attempts == '':
-            self.max_attempts = None
-
         # Need the problem location in openendedresponse to send out.  Adding
         # it to the system here seems like the least clunky way to get it
         # there.
@@ -391,7 +388,7 @@ class CapaModule(CapaFields, XModule):
 
         content = {'name': self.display_name_with_default,
                    'html': html,
-                   'weight': self.descriptor.weight,
+                   'weight': self.weight,
                    }
 
         context = {'problem': content,