str2decimal: don't return a negative zero

mysql-test/r/type_decimal.result

@@ -221,7 +221,6 @@ drop  table t1;
 create table t1 (a decimal(10,2) unsigned);
 insert into t1 values ("0.0"),("-0.0"),("+0.0"),("01.0"),("+01.0"),("-01.0");
 Warnings:
-Warning	1264	Out of range value for column 'a' at row 2
 Warning	1264	Out of range value for column 'a' at row 6
 insert into t1 values ("-.1"),("+.1"),(".1");
 Warnings:
@@ -280,7 +279,6 @@ drop  table t1;
 create table t1 (a decimal(10,2) zerofill);
 insert into t1 values ("0.0"),("-0.0"),("+0.0"),("01.0"),("+01.0"),("-01.0");
 Warnings:
-Warning	1264	Out of range value for column 'a' at row 2
 Warning	1264	Out of range value for column 'a' at row 6
 insert into t1 values ("-.1"),("+.1"),(".1");
 Warnings:

storage/tokudb/mysql-test/tokudb/r/type_decimal.result

@@ -222,7 +222,6 @@ drop  table t1;
 create table t1 (a decimal(10,2) unsigned);
 insert into t1 values ("0.0"),("-0.0"),("+0.0"),("01.0"),("+01.0"),("-01.0");
 Warnings:
-Warning	1264	Out of range value for column 'a' at row 2
 Warning	1264	Out of range value for column 'a' at row 6
 insert into t1 values ("-.1"),("+.1"),(".1");
 Warnings:
@@ -281,7 +280,6 @@ drop  table t1;
 create table t1 (a decimal(10,2) zerofill);
 insert into t1 values ("0.0"),("-0.0"),("+0.0"),("01.0"),("+01.0"),("-01.0");
 Warnings:
-Warning	1264	Out of range value for column 'a' at row 2
 Warning	1264	Out of range value for column 'a' at row 6
 insert into t1 values ("-.1"),("+.1"),(".1");
 Warnings:

strings/decimal.c

@@ -928,6 +928,8 @@ internal_str2dec(const char *from, decimal_t *to, char **end, my_bool fixed)
         error= decimal_shift(to, (int) exponent);
     }
   }
+  if (to->sign && decimal_is_zero(to))
+    to->sign= 0;
   return error;
 
 fatal_error: