lib/printf-format-fix: fix rejection of "%.0f" as a valid string

Sometimes you want to calculate in floats, but don't want the decimals
printed.

Signed-off-by: Phil Carmody <phil@dovecot.fi>

src/lib/printf-format-fix.c

@@ -38,11 +38,12 @@ static bool verify_length(const char **p)
 		/* We don't bother supporting "*m$" - it's not used
 		   anywhere and seems a bit dangerous. */
 		*p += 1;
-	} else if (**p >= '1' && **p <= '9') {
+	} else if (**p >= '0' && **p <= '9') {
 		/* Limit to 4 digits - we'll never want more than that.
 		   Some implementations might not handle long digits
 		   correctly, or maybe even could be used for DoS due
-		   to using too much CPU. */
+		   to using too much CPU. If you want to express '99'
+		   as '00099', then you lose in this function. */
 		unsigned int i = 0;
 		do {
 			*p += 1;

src/lib/test-printf-format-fix.c

@@ -25,6 +25,7 @@ static void test_unchanged()
 		"Precision %.9999s",
 		"Precision %1.9999s",
 		"Precision parameter %1.*s %.*s",
+		"Floating precisions such as %.0f %0.4f %-4.0f",
 		"Length modifiers %hd %hhd %ld %lld %Lg %jd %zd %td",
 		"Specifiers %s %u %d %c %i %x %X %p %o %e %E %f %F %g %G %a %A",
 		"%%doesn't cause confusion in %%m and %%n",