[5.1] Quote user-supplied content for use in preg_match

[vlakoff]

Follow-up to #13039.

Escaping for use in regex as it should be.

Removed the error suppression as it shouldn't be needed now.
It was just a "poor man fix", and there is no @preg_* elsewhere in the code.

[GrahamCampbell]

This is not really correct. If quoting is needed, then the input is already invalid...

[vlakoff]

• For example the dot in "application/vnd.ms-excel" is interpreted as a meta character. Doesn't change anything in practice, but just to show it's wrong. Not the first time I see this.
• Currently someone could pass expensive regexes. Needless to say, this hurts.

[GrahamCampbell]

Good point. 👍, but I'd say just do the quoting inline. Don't write to the array again.

[GrahamCampbell]

Please add a test case which failed before and passes now.

[vlakoff]

• Personally I prefer the quoting as it is, rather than inlining it.
• Added dedicated tests.