bug fixes to density lookup

ChemID.py

@@ -499,8 +499,8 @@ def string2density(string):
                             for k in j['Section']:
                                 if k['TOCHeading'] == 'Density':
                                     for ii in k['Information']:
-                                        rho_string = ii['Value']['StringWithMarkup'][0]['String']
                                         try:
+                                            rho_string = ii['Value']['StringWithMarkup'][0]['String']
                                             tmp_rho = re.match('(?:\d+(?:\.\d*)?|\.\d+)',rho_string)
                                             tmp_rho = float(tmp_rho.group())
                                             rho_list.append(tmp_rho)