Auto suggestion error when type "\\" character

[toanvan]

I found a bug the same with issue #570 but with \\ characters and when insert \\ to command.
For example:

1. The first case:
   $ \\
   (logout and show error)
   =>log file

java.lang.StringIndexOutOfBoundsException: String index out of range: -1
        at java.lang.String.substring(String.java:1931) ~[na:1.8.0_261]
        at org.jline.reader.impl.LineReaderImpl.matchPreviousCommand(LineReaderImpl.java:3985) ~[jline-3.17.1.jar:na]
        at org.jline.reader.impl.LineReaderImpl.getDisplayedBufferWithPrompts(LineReaderImpl.java:4011) ~[jline-3.17.1.jar:na]

2. The second case:
   $appendcommand \l
   Insert slash to above command
   $appendcommand \\l
   (logout and show error)
   =>log file

java.util.regex.PatternSyntaxException: Illegal/unsupported escape sequence near index 17
appendcluster \\\l.*
                 ^
        at java.util.regex.Pattern.error(Pattern.java:1969) ~[na:1.8.0_261]
        at java.util.regex.Pattern.escape(Pattern.java:2485) ~[na:1.8.0_261]
        at java.util.regex.Pattern.atom(Pattern.java:2212) ~[na:1.8.0_261]
        at java.util.regex.Pattern.sequence(Pattern.java:2144) ~[na:1.8.0_261]
        at java.util.regex.Pattern.expr(Pattern.java:2010) ~[na:1.8.0_261]
        at java.util.regex.Pattern.compile(Pattern.java:1702) ~[na:1.8.0_261]

Please help me check again