Custom and wrong number formats not read

```
What steps will reproduce the problem?

1.Use a sheet with custom number formats in cell. When the syntax of the format
is wrong, the
lib doesn't read the value of the cell.

What is the expected output? What do you see instead?
Instead of reading the cell's value, it outputs the actual (wrong) syntax of
the number format.

Please provide any additional information below.
For instance i received a spreadsheet from a customer with custom number
formats: ???, ????, ???
??. Now, for all the cells that use these formats, the class returns ???, ????,
?????.

Anyone had the same problem? I know I could just remove all the formats, but it
should be
automated somehow in my project, because the files are sent by machines not by
users.

THANKS !
```

Original issue reported on code.google.com by `attana...@gmail.com` on 14 Oct 2009 at 1:26

Start by reproducing the issue with a spreadsheet containing malformed custom number formats, including the examples in the report. Trace the cell-value reading path and verify that cells using invalid formats return their values rather than the format syntax; no file or test location is named in the issue.

Written by the indexing model from the issue text.