fix #520 datetime fractional seconds part error

Author: zhaoyk

ext/mysql2/result.c

@@ -294,9 +294,10 @@ static VALUE rb_mysql_result_fetch_row(VALUE self, ID db_timezone, ID app_timezo
         case MYSQL_TYPE_DATETIME: { /* DATETIME field */
           int tokens;
           unsigned int year=0, month=0, day=0, hour=0, min=0, sec=0, msec=0;
+          char msec_char[7] = {'0','0','0','0','0','0','\0'};
           uint64_t seconds;
 
-          tokens = sscanf(row[i], "%4u-%2u-%2u %2u:%2u:%2u.%6u", &year, &month, &day, &hour, &min, &sec, &msec);
+          tokens = sscanf(row[i], "%4u-%2u-%2u %2u:%2u:%2u.%6s", &year, &month, &day, &hour, &min, &sec, msec_char);
           if (tokens < 6) { /* msec might be empty */
             val = Qnil;
             break;
@@ -324,7 +325,19 @@ static VALUE rb_mysql_result_fetch_row(VALUE self, ID db_timezone, ID app_timezo
                     val = rb_funcall(val, intern_new_offset, 1, opt_utc_offset);
                   }
                 }
-              } else { /* use Time, supports microseconds */
+              } else {
+                /* microseconds can be up to 6 digits. Fewer digits must be interpreted from
+                 * the left because the microseconds are to the right of the decimal point.
+                 */
+                if (tokens == 7) {
+                  int i;
+                  for (i = 0; i < 6; ++i) {
+                    if (msec_char[i] == '\0') {
+                      msec_char[i] = '0';
+                    }
+                  }
+                  msec = (unsigned int)strtoul(msec_char, NULL, 10);
+                }
                 val = rb_funcall(rb_cTime, db_timezone, 7, UINT2NUM(year), UINT2NUM(month), UINT2NUM(day), UINT2NUM(hour), UINT2NUM(min), UINT2NUM(sec), UINT2NUM(msec));
                 if (!NIL_P(app_timezone)) {
                   if (app_timezone == intern_local) {