Bug#43833 Simple INSERT crashes the server

The crash happens due to wrong 'digits' variable value(0),
'digits' can not be 0, so the fix is use 1 as min allowed value.

mysql-test/r/insert.result

@@ -595,4 +595,9 @@ SELECT * FROM t2;
 c1
 15449237462
 DROP TABLE t1, t2;
+CREATE TABLE t1(f1 FLOAT);
+INSERT INTO t1 VALUES (1.23);
+CREATE TABLE t2(f1 CHAR(1));
+INSERT INTO t2 SELECT f1 FROM t1;
+DROP TABLE t1, t2;
 End of 5.0 tests.

mysql-test/t/insert.test

@@ -454,5 +454,14 @@ SELECT * FROM t2;
 
 DROP TABLE t1, t2;
 
+#
+# Bug#43833 Simple INSERT crashes the server
+#
+CREATE TABLE t1(f1 FLOAT);
+INSERT INTO t1 VALUES (1.23);
+CREATE TABLE t2(f1 CHAR(1));
+INSERT INTO t2 SELECT f1 FROM t1;
+DROP TABLE t1, t2;
+
 --echo End of 5.0 tests.
 

sql/field.cc

@@ -5987,13 +5987,13 @@ int Field_str::store(double nr)
     calculate the maximum number of significant digits if the 'f'-format
     would be used (+1 for decimal point if the number has a fractional part).
   */
-  digits= max(0, (int) max_length - fractional);
+  digits= max(1, (int) max_length - fractional);
   /*
     If the exponent is negative, decrease digits by the number of leading zeros
     after the decimal point that do not count as significant digits.
   */
   if (exp < 0)
-    digits= max(0, (int) digits + exp);
+    digits= max(1, (int) digits + exp);
   /*
     'e'-format is used only if the exponent is less than -4 or greater than or
     equal to the precision. In this case we need to adjust the number of
@@ -6001,7 +6001,7 @@ int Field_str::store(double nr)
     We also have to reserve one additional character if abs(exp) >= 100.
   */
   if (exp >= (int) digits || exp < -4)
-    digits= max(0, (int) (max_length - 5 - (exp >= 100 || exp <= -100)));
+    digits= max(1, (int) (max_length - 5 - (exp >= 100 || exp <= -100)));
 
   /* Limit precision to DBL_DIG to avoid garbage past significant digits */
   set_if_smaller(digits, DBL_DIG);