Generating field text fails if max length is less than 6

Problem/Motivation

When the maximum length of a text field is set to less than 6 the _text_devel_generate() function will throw an error:
Warning: mt_rand(): max(0) is smaller than min(1) in _text_devel_generate()

This is because the max value is the max_length divided by six, implicitly cast to an int.

Proposed resolution

Use the ceil() function to ensure the division provides a max of at least 1 on max_lengths greater than 0.

Remaining tasks

Patch needs review.

User interface changes

N/A

API changes

N/A

Data model changes

N/A