MDEV-25808 PREPARE/EXECUTE makes signed integer out of unsigned

Closes #1844

mysql-test/main/prepare.result

@@ -50,3 +50,17 @@ t1_first
 deallocate prepare stmt1;
 deallocate prepare stmt2;
 drop table t1;
+#
+# MDEV-25808 PREPARE/EXECUTE makes signed integer out of unsigned
+#
+prepare p1 from 'select concat(?)';
+execute p1 using 17864960750176564435;
+concat(?)
+17864960750176564435
+prepare p1 from 'select SQRT(?) is not null';
+execute p1 using 17864960750176564435;
+SQRT(?) is not null
+1
+#
+# End of 10.3 tests
+#

mysql-test/main/prepare.test

@@ -40,3 +40,15 @@ execute stmt2;
 deallocate prepare stmt1;
 deallocate prepare stmt2;
 drop table t1;
+
+--echo #
+--echo # MDEV-25808 PREPARE/EXECUTE makes signed integer out of unsigned
+--echo #
+prepare p1 from 'select concat(?)';
+execute p1 using 17864960750176564435;
+prepare p1 from 'select SQRT(?) is not null';
+execute p1 using 17864960750176564435;
+
+--echo #
+--echo # End of 10.3 tests
+--echo #

sql/item.cc

@@ -4592,13 +4592,15 @@ bool Item_param::get_date(MYSQL_TIME *res, ulonglong fuzzydate)
 }
 
 
-double Item_param::PValue::val_real() const
+double Item_param::PValue::val_real(const Type_std_attributes *attr) const
 {
   switch (type_handler()->cmp_type()) {
   case REAL_RESULT:
     return real;
   case INT_RESULT:
-    return (double) integer;
+    return attr->unsigned_flag
+      ? (double) (ulonglong) integer
+      : (double) integer;
   case DECIMAL_RESULT:
   {
     double result;
@@ -4680,7 +4682,7 @@ String *Item_param::PValue::val_str(String *str,
     str->set_real(real, NOT_FIXED_DEC, &my_charset_bin);
     return str;
   case INT_RESULT:
-    str->set(integer, &my_charset_bin);
+    str->set_int(integer, attr->unsigned_flag, &my_charset_bin);
     return str;
   case DECIMAL_RESULT:
     if (my_decimal2string(E_DEC_FATAL_ERROR, &m_decimal, 0, 0, 0, str) <= 1)

sql/item.h

@@ -3565,7 +3565,7 @@ class Item_param :public Item_basic_value,
       m_string.swap(other.m_string);
       m_string_ptr.swap(other.m_string_ptr);
     }
-    double val_real() const;
+    double val_real(const Type_std_attributes *attr) const;
     longlong val_int(const Type_std_attributes *attr) const;
     my_decimal *val_decimal(my_decimal *dec, const Type_std_attributes *attr);
     String *val_str(String *str, const Type_std_attributes *attr);
@@ -3619,7 +3619,7 @@ class Item_param :public Item_basic_value,
 
   double val_real()
   {
-    return can_return_value() ? value.val_real() : 0e0;
+    return can_return_value() ? value.val_real(this) : 0e0;
   }
   longlong val_int()
   {