str-bytes-safe displays position in line incorrectly

[jolaf]

The following code:

s = '%s%s' % (b''.decode(), b'')

produces the following output:

$ python3 Test.py
$ mypy --show-column-numbers --pretty --show-error-codes Test.py 
Test.py:1:15: error: On Python 3 '%s' % b'abc' produces "b'abc'"; use %r if this is a desired behavior  [str-bytes-safe]
    s = '%s%s' % (b''.decode(), b'')
                  ^
Found 1 error in 1 file (checked 1 source file)
$ mypy --version
mypy 0.740
$ python3 --version
Python 3.6.8

Note that the indicated position of the error in the line is pointing to the first argument (b''.decode()) instead of the seconds one (b'') which is highly misleading.

[ilevkivskyi]

Duplicate of #7528