fixes #26183; wordwrap: flush lastSep before splitting an overlong word (#26184)

wrapWords(splitLongWords = true) dropped the separator before a word it
had to split, fusing it with the word before it. Flush lastSep first,
the same as the branch that handles a word which fits.

Updates twordwrap's longlongwordRes fixture, which was pinned against
the old behavior at three points where a source line break normalizes to
a synthetic space.

lib/std/wordwrap.nim

@@ -53,6 +53,8 @@ proc wrapWords*(s: string, maxLineWidth = 80,
       let wlen = olen(s, i, j)
       if wlen > spaceLeft:
         if splitLongWords and wlen > maxLineWidth:
+          if lastSep.len > 0 and spaceLeft > 0:
+            result.add(lastSep)
           var k = 0
           while k < j - i:
             if spaceLeft <= 0:

tests/stdlib/twordwrap.nim

@@ -29,11 +29,11 @@ iaoenvlcyfglwckßqfgvwkßqgfvlwkßqfgvlwckßqvlwkgfUIαοιαοιαχολωχσ
 ξχλωωχαοεοιαεοαεοιαεοαεοιαοεσναοεκνρκψγκψφϵιηαααοε"""
 let longlongwordRes = """
 abc uitdaeröägfßhydüäpydqfü,träpydqgpmüdträpydföägpydörztdüöäfguiaeowäzjdtrüöäp
-psnrtuiydrözenrüöäpyfdqazpesnrtulocjtüöäzydgyqgfqfgprtnwjlcydkqgfüöezmäzydydqüü
+psnrtuiydrözenrüöäpyfdqazpesnrtulocjtüö äzydgyqgfqfgprtnwjlcydkqgfüöezmäzydydqüü
 öäpdtrnvwfhgckdumböäpydfgtdgfhtdrntdrntydfogiayqfguiatrnydrntüöärtniaoeydfgaoeiq
-fglwcßqfgxvlcwgtfhiaoenrsüöäapmböäptdrniaoydfglckqfhouenrtsüöäptrniaoeyqfgulocf
+fglwcßqfgxvlcwgtfhiaoen rsüöäapmböäptdrniaoydfglckqfhouenrtsüöäptrniaoeyqfgulocf
 qclgwxßqflgcwßqfxglcwrniatrnmüböäpmöäbpümöäbpüöämpbaoestnriaesnrtdiaesrtdniaesdr
-tnaetdriaoenvlcyfglwckßqfgvwkßqgfvlwkßqfgvlwckßqvlwkgfUIαοιαοιαχολωχσωχνωκψρχκψ
+tnaetdr iaoenvlcyfglwckßqfgvwkßqgfvlwkßqfgvlwckßqvlwkgfUIαοιαοιαχολωχσωχνωκψρχκψ
 ρτιεαοσηζϵηζιοεννκεωνιαλωσωκνκψρκγτφγτχκγτεκργτιχνκιωχσιλωσλωχξλξλξωχωχ
 ξχλωωχαοεοιαεοαεοιαεοαεοιαοεσναοεκνρκψγκψφϵιηαααοε"""
 doAssert wrapWords(longlongword) == longlongwordRes