[perl #132041] [UNI] Str.perl fails to escape certain lone diacritics at the start of the string.

[via RT]

# New Ticket Created by  Sam S. 
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Some diacritical marks are correctly escaped by `.perl` when they appear 
at the beginning of the string:

     ➜  say "\c[COMBINING DIAERESIS]".perl;             # "\x[308]"

     ➜  say "a" ~ "\c[COMBINING DIAERESIS]".perl.EVAL;  # ä

But the following one is rendered as part of the opening quote's 
grapheme, causing EVAL to not roundtrip:

     ➜  say "\c[TELUGU VOWEL SIGN AA]".perl;        # "ా"
     ➜  say "\c[TELUGU VOWEL SIGN AA]".perl.chars;  # 2

     ➜  say "a" ~ "\c[TELUGU VOWEL SIGN AA]".perl.EVAL;
     ===SORRY!=== Error while compiling /home/[...]/EVAL_0
     Bogus statement
     at /home/[...]/EVAL_0:1
     ------> <BOL>⏏"ా"
         expecting any of:
             prefix
             term

Note that both of the marks demonstrated above are in the same Unicode 
category:

     ➜  say uniprops "\c[COMBINING DIAERESIS]";
     (Mn)

     ➜  say uniprops "\c[TELUGU VOWEL SIGN AA]";
     (Mn)


(This bug was found via the following SO answer: 
https://stackoverflow.com/a/46042910/1160124)

---
This is Rakudo version 2017.08-86-gbfee5a1ed built on MoarVM version 
2017.08.1-128-gde6dceda
implementing Perl 6.c.