Fix bug in wxNumberFormatter::ToString() for negative numbers.

Don't include the possible leading sign in the span of digits to be grouped as
this gave nonsensical strings such as "-,123" when adding thousands separators
to "123".

Closes #14526.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72256 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/numformatter.cpp

@@ -235,6 +235,10 @@ void wxNumberFormatter::AddThousandsSeparators(wxString& s)
         pos = s.length();
     }
 
+    // End grouping at the beginning of the digits -- there could be at a sign
+    // before their start.
+    const size_t start = s.find_first_of("0123456789");
+
     // We currently group digits by 3 independently of the locale. This is not
     // the right thing to do and we should use lconv::grouping (under POSIX)
     // and GetLocaleInfo(LOCALE_SGROUPING) (under MSW) to get information about
@@ -242,7 +246,7 @@ void wxNumberFormatter::AddThousandsSeparators(wxString& s)
     // wxLocale level first and then used here in the future (TODO).
     const size_t GROUP_LEN = 3;
 
-    while ( pos > GROUP_LEN )
+    while ( pos > start + GROUP_LEN )
     {
         pos -= GROUP_LEN;
         s.insert(pos, thousandsSep);