Incorrect help message for short options with paramLabel when arity > 1

[remkop]

This only happens for short options, not when an option has either both a short and a long option or just long options.

The help message looks like this. Note the double = and the missing opening square bracket [ in the options list:

Usage: <main class> [-f[=FILE...]] [-P[=KEY=VALUE...]] 
  -f= =FILE...]               files
  -P= =KEY=VALUE...]          Project properties (key-value pairs)

When a long option is specified, or arity=1, things look okay:

Usage: <main class> [-f=FILE] [-P[=KEY=VALUE...]]
  -f= FILE                    a file
  -P, --properties[=KEY=VALUE...]
                              Project properties (key-value pairs)

[remkop]

Index: src/main/java/picocli/CommandLine.java
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- src/main/java/picocli/CommandLine.java	(revision )
+++ src/main/java/picocli/CommandLine.java	(revision )
@@ -2990,7 +2990,10 @@
                 // if no long option, fill in the space between the short option name and the param label value
                 if (paramLabelText.length > 0 && longOption.length() == 0) {
                     sep = paramLabelRenderer.separator();
-                    paramLabelText = paramLabelText.substring(sep.length());
+                    // #181 paramLabelText may be =LABEL or [=LABEL...]
+                    int sepStart = paramLabelText.plainString().indexOf(sep);
+                    Text prefix = paramLabelText.substring(0, sepStart);
+                    paramLabelText = prefix.append(paramLabelText.substring(sepStart + sep.length()));
                 }
                 Text longOptionText = scheme.optionText(longOption);
                 longOptionText = longOptionText.append(paramLabelText);