fix strftime field widths with %F format and zero year
the code to strip initial sign and leading zeros inadvertently
stripped all the zeros and the subsequent '-' separating the month.
instead, only strip sign characters from the very first position, and
only strip zeros when they are followed by another digit.
based on testing by Dennis Wölfing.
diff --git a/src/time/strftime.c b/src/time/strftime.c
index d1ca7ca..16b3bb2 100644
--- a/src/time/strftime.c
+++ b/src/time/strftime.c
@@ -251,7 +251,8 @@
t = __strftime_fmt_1(&buf, &k, *f, tm, loc, pad);
if (!t) break;
if (width) {
- for (; *t=='+' || *t=='-' || (*t=='0'&&t[1]); t++, k--);
+ if (*t=='+' || *t=='-') t++, k--;
+ for (; *t=='0' && t[1]-'0'<10U; t++, k--);
width--;
if (plus && tm->tm_year >= 10000-1900)
s[l++] = '+';