This is a regression caused by MDL-67934, and I am currently sitting in awe of our tester.

1. Create a question with idnumber '1.0E+29'
2. Click duplicate.
3. Click Save changes.

Actual result: Debug info: ERROR: duplicate key value violates unique constraint "q_ques_catidn_uix"
DETAIL: Key (category, idnumber)=(1, 1.0E+29) already exists.

Expected result: at step 2) the suggested idnumber for the duplicate question should be '1.0E+30' - idnumbers are strings, and we increment the final number-like part of it, if possible. This is not a float.