decimal: *correct* implementation of ROUND_UP at last

mysql-test/r/type_newdecimal.result

@@ -1994,3 +1994,6 @@ select 0.000000000000000000000000000000000000000000000000001 mod 1;
 select 0.0000000001 mod 1;
 0.0000000001 mod 1
 0.0000000001
+select 0.01 mod 1;
+0.01 mod 1
+0.01

mysql-test/t/type_newdecimal.test

@@ -1579,3 +1579,5 @@ select 0.000000000000000000000000000000000000000000000000001 mod 1;
 # incorrect result
 #
 select 0.0000000001 mod 1;
+select 0.01 mod 1;
+

strings/decimal.c

@@ -137,7 +137,7 @@ static const dec1 frac_max[DIG_PER_DEC1-1]={
 
 static inline int ROUND_UP(int x)
 {
-  return (x + (x > 0 ? 1 : -1) * (DIG_PER_DEC1 - 1)) / DIG_PER_DEC1;
+  return (x + (x > 0 ? DIG_PER_DEC1 - 1 : 0)) / DIG_PER_DEC1;
 }
 
 #ifdef HAVE_valgrind