release script: Fix inconsequential bug.

* The prefix separation was meant to speed up the pattern matching
  and eventually ensure substitution only happens once.

scripts/release/make-distcheck

@@ -34,7 +34,7 @@ errMsg()
   typeset cmd=$BASH_COMMAND pfx
   typeset -i ofs=0 vpos src_lev=${#BASH_SOURCE[@]}
   while [[ "${cmd:$ofs}" =~ \$\{([a-zA-Z_][a-zA-Z_0-9]*)\} ]]; do
-    pfx=${cmd:ofs}; vpos=${vpos%%\$*}; ofs=$((ofs+${#vpos}))
+    pfx=${cmd:ofs}; vpos=${pfx%%\$*}; ofs=$((ofs+${#vpos}))
     cmd=${cmd/\$\{${BASH_REMATCH[1]}\}/${!BASH_REMATCH[1]}}
   done
   printf 'error: failed to run command\n%s\nat %s, line %d!\n' "$cmd" \

scripts/release/make-release

@@ -43,7 +43,7 @@ errMsg()
   typeset cmd=$BASH_COMMAND pfx
   typeset -i ofs=0 vpos src_lev=${#BASH_SOURCE[@]}
   while [[ "${cmd:$ofs}" =~ \$\{([a-zA-Z_][a-zA-Z_0-9]*)\} ]]; do
-    pfx=${cmd:ofs}; vpos=${vpos%%\$*}; ofs=$((ofs+${#vpos}))
+    pfx=${cmd:ofs}; vpos=${pfx%%\$*}; ofs=$((ofs+${#vpos}))
     cmd=${cmd/\$\{${BASH_REMATCH[1]}\}/${!BASH_REMATCH[1]}}
   done
   printf 'error: failed to run command\n%s\nat %s, line %d!\n' "$cmd" \