[BUGFIX] Respect line breaks in stdWrap.cropHTML

By using the PCRE_DOTALL (/s) pattern modifier in the cropHTML
regular expression for preserving HTML entities the dot in the
pattern will include line breaks.
Resolves: #28741
Releases: 6.1, 6.0, 4.7, 4.5

Change-Id: If1047d4d0a42ee1149e670b757bbb4b216ae101d
Reviewed-on: https://review.typo3.org/19500
Reviewed-by: Benjamin Mack
Tested-by: Benjamin Mack