tei2txt.xsl: use for-each instead of recursive template

[bertsky]

Here's another one:

runtime error: file /usr/local/share/perl/5.26.1/auto/share/dist/DTA-TEI-Text/xslt/tei2txt.xsl line 479 element value-of
xsltApplySequenceConstructor: A potential infinite template recursion was detected.
You can adjust xsltMaxDepth (--maxdepth) in order to raise the maximum number of nested template calls and variables/params (currently set to 250).
Templates:
#0 name output_gap 
#1 name output_gap 
#2 name output_gap 
#3 name output_gap 
#4 name output_gap 
#5 name output_gap 
#6 name output_gap 
#7 name output_gap 
#8 name output_gap 
#9 name output_gap 
#10 name output_gap 
#11 name output_gap 
#12 name output_gap 
#13 name output_gap 
#14 name output_gap 
Variables:
#0
recLevel 
output 
#1
output 
#2
recLevel 
output 
#3
output 
#4
recLevel 
output 
#5
output 
#6
recLevel 
output 
#7
output 
#8
recLevel 
output 
#9
output 
#10
recLevel 
output 
#11
output 
#12
recLevel 
output 
#13
output 
#14
recLevel 
output 
 at /usr/local/share/perl/5.26.1/DTA/TEI/Text/Transform.pm line 205.

So clearly, although none of our @quantity values surpasses the mentioned limit of xsltMaxDepth=250, we get an ugly warning here.

This happens with libxml2==2.9.4.

I found no proper replacement in XSLT 1.1 for the repeated gap_char output, but this hack serves its purpose.