allow chop to take an empty string (#31312)

Author: bicycle1885

base/strings/util.jl

@@ -96,6 +96,9 @@ julia> chop(a, head = 5, tail = 5)
 ```
 """
 function chop(s::AbstractString; head::Integer = 0, tail::Integer = 1)
+    if isempty(s)
+        return SubString(s)
+    end
     SubString(s, nextind(s, firstindex(s), head), prevind(s, lastindex(s), tail))
 end
 

test/strings/util.jl

@@ -302,6 +302,7 @@ end
     @test chomp("foo\r\n") == "foo"
     @test chomp("fo∀\r\n") == "fo∀"
     @test chomp("fo∀") == "fo∀"
+    @test chop("") == ""
     @test chop("fooε") == "foo"
     @test chop("foεo") == "foε"
     @test chop("∃∃∃∃") == "∃∃∃"