'main': Fix an infinite loop.

On the test case, the behaviour was as follows:

+highlighters/main/main-highlighter.zsh:733> _zsh_highlight_main_highlighter__try_expand_parameter '$1'
+highlighters/main/main-highlighter.zsh:432> local arg='$1'
+highlighters/main/main-highlighter.zsh:433> unset reply
+highlighters/main/main-highlighter.zsh:439> local -a match mbegin mend
+highlighters/main/main-highlighter.zsh:440> local MATCH
+highlighters/main/main-highlighter.zsh:440> integer MBEGIN MEND
+highlighters/main/main-highlighter.zsh:441> local parameter_name
+highlighters/main/main-highlighter.zsh:442> local -a words
+highlighters/main/main-highlighter.zsh:443> [[ '$' != \$ ]]
+highlighters/main/main-highlighter.zsh:446> [[ 1 == { ]]
+highlighters/main/main-highlighter.zsh:449> parameter_name=1
+highlighters/main/main-highlighter.zsh:451> [[ none == none ]]
+highlighters/main/main-highlighter.zsh:451> zmodload -e zsh/parameter
+highlighters/main/main-highlighter.zsh:452> [[ ${parameter_name} -regex-match ^${~parameter_name_pattern}$ ]]
+highlighters/main/main-highlighter.zsh:453> [[ '' != *special* ]]
+highlighters/main/main-highlighter.zsh:456> case array-special (*array*|*assoc*)
+highlighters/main/main-highlighter.zsh:458> words=( '$1' )
+highlighters/main/main-highlighter.zsh:469> reply=( '$1' )

There are two problems here:

- In terms of _zsh_highlight_main_highlighter__try_expand_parameter's
  pre- and postconditions, the expansion of the word «$1» (line 733)
  included that same word (line 469).

  That happened because word-to-be-expanded is passed to
  _zsh_highlight_main_highlighter__try_expand_parameter as its first
  positional parameter, and in this case the word happened to be «$1».

- Furthermore, the exclusion of special parameters (line 453) false
  negatived.  That happened because $parameter_name_pattern explicitly
  allows positional parameters, but ${parameters[(e)1]} expands to
  nothing.  This will be fixed in the next commit.

Not a regression from 0.7.1.

Author: danielshahaf

highlighters/main/main-highlighter.zsh

@@ -730,7 +730,7 @@ _zsh_highlight_main_highlighter_highlight_list()
     fi
 
     # Expand parameters.
-    if _zsh_highlight_main_highlighter__try_expand_parameter "$arg"; then
+    if (( ! in_param )) && _zsh_highlight_main_highlighter__try_expand_parameter "$arg"; then
       # That's not entirely correct --- if the parameter's value happens to be a reserved
       # word, the parameter expansion will be highlighted as a reserved word --- but that
       # incorrectness is outweighed by the usability improvement of permitting the use of