Removed the underflow check (bug #22129)

mysql-test/r/type_float.result:
  Fixed the testcase
strings/strtod.c:
  Removed the underflow check

mysql-test/r/type_float.result

@@ -274,7 +274,7 @@ a	double			0
 drop table t1,t2,t3;
 select 1e-308, 1.00000001e-300, 100000000e-300;
 1e-308	1.00000001e-300	100000000e-300
-0	1.00000001e-300	1e-292
+1e-308	1.00000001e-300	1e-292
 select 10e307;
 10e307
 1e+308

strings/strtod.c

@@ -31,7 +31,6 @@
 
 #define MAX_DBL_EXP	308
 #define MAX_RESULT_FOR_MAX_EXP 1.7976931348623157
-#define MIN_RESULT_FOR_MIN_EXP 2.225073858507202
 static double scaler10[] = {
   1.0, 1e10, 1e20, 1e30, 1e40, 1e50, 1e60, 1e70, 1e80, 1e90
 };
@@ -161,28 +160,17 @@ double my_strtod(const char *str, char **end_ptr, int *error)
     order= exp + (neg_exp ? -1 : 1) * (ndigits - 1);
     if (order < 0)
       order= -order;
-    if (order >= MAX_DBL_EXP && result)
+    if (order >= MAX_DBL_EXP && !neg_exp && result)
     {
       double c;
       /* Compute modulus of C (see comment above) */
       c= result / scaler * 10.0;
-      if (neg_exp)
-      {
-        if (order > MAX_DBL_EXP || c < MIN_RESULT_FOR_MIN_EXP)
-        {
-          result= 0.0;
-          goto done;
-        }
-      }
-      else
-      {
       if (order > MAX_DBL_EXP || c > MAX_RESULT_FOR_MAX_EXP)
       {
         overflow= 1;
         goto done;
       }
     }
-    }
 
     exp= tmp_exp;
     if (exp < 0)