Fix numFmtID when chk_exists returns None

cellXfs._attrs['applyNumberFormat'].value returns a literal 'true' or 'false' which throws an error when int() is called. Switch numFmtId = int(cellXfs._attrs['applyNumberFormat'].value) to numFmtId = int(cellXfs._attrs['applyNumberFormat'].value == 'true')

xlsx2csv.py

@@ -528,7 +528,7 @@ def parse(self, filehandle):
                 if cellXfs._attrs and 'numFmtId' in cellXfs._attrs:
                     numFmtId = int(cellXfs._attrs['numFmtId'].value)
                     if self.chk_exists(numFmtId) == None:
-                        numFmtId = int(cellXfs._attrs['applyNumberFormat'].value)
+                        numFmtId = int(cellXfs._attrs['applyNumberFormat'].value == 'true')
                     self.cellXfs.append(numFmtId)
                 else:
                     self.cellXfs.append(None)