[flang][runtime] Fix handling of output FORMAT('x' 'y')

[klausler]

Summary

I'm emitting "x'y" because the space-separated apostrophes are
misinterpreted as being adjacent repeated quotation marks.
Fix to ensure no space skipping is applied when checking for
repeated quotation marks.

flang/runtime/format-implementation.h

if (ch == '(') {
         ReportBadFormat(context,
             "FORMAT missing closing quote on character literal",
             maybeReversionPoint);
         return 0;
       }
       ++offset_;
       std::size_t chars{
           static_cast<std::size_t>(&format_[offset_] - &format_[start])};
-      if (PeekNext() == quote) {
+      if (offset_ < formatLength_ && format_[offset_] == quote) {
         // subtle: handle doubled quote character in a literal by including
         // the first in the output, then treating the second as the start
         // of another character literal.
       } else {
         --chars;
       }
       context.Emit(format_ + start, chars);
     } else if (ch == 'H') {