[m-rev.] Trivial diff: bugfix for string.base_string_to_int

[Ralph Becket]

Estimated hours taken: 0.1
Branches: main

Fixed a bug in string.base_string_to_int/3.

library/string.m:
	Bugfix for string.base_string_to_int/3 (and consequently
	string.to_int/2 and string.det_to_int/1) preventing the strings "+" and
	"-" being interpreted as 0.  string.base_string_to_int/3 now requires
	the string to contain at least one digit.

I accidentally checked this on in before taking a diff, but the change
is to add the two `Len > 1' subgoals:

string__base_string_to_int(Base, String, Int) :-
        string__index(String, 0, Char),
        Len = string__length(String),
        ( Char = ('-') ->
                Len > 1,
                foldl_substring(accumulate_int(Base), String, 1, Len - 1, 0, N),
                Int = -N
        ; Char = ('+') ->
                Len > 1,
                foldl_substring(accumulate_int(Base), String, 1, Len - 1, 0, N),
                Int = N
        ;
                foldl_substring(accumulate_int(Base), String, 0, Len, 0, N),
                Int = N
        ).

-- Ralph
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