Merge r1599012, r1601559, r1818624, r1819969, r1819970 from trunk:

Merge r1599012, r1601559, r1818624, r1819969, r1819970 from trunk:

mod_proxy_html: skip documents < 4 bytes
PR 56286
Micha Lenk

follow up r1599012:
C99 fix

Fix some style

mod_proxy_html: follow up to r1599012.

To determine whether or not HTML data are lower than 4 bytes, use a retain
buffer rather than assuming that all should be contained in a single bucket
with the next one being EOS (if any).

mod_proxy_html: don't depend on NUL terminated bucket data.

ap_regexec() wants NUL terminated strings, so use ap_regexec_len() instead.

Submitted by: niq, takashi, jailletc36, ylavic, ylavic
Reviewed by: jim, ylavic, icing

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1821073 13f79535-47bb-0310-9956-ffa450edef68