MDEV-21127 Assertion failed in key_text::key_text

Wrong condition for corner values.

mysql-test/suite/innodb/r/innodb-fk.result

@@ -199,3 +199,10 @@ b char(255),
 FOREIGN KEY ( a012345678901234567890123456789012345678901, b ) REFERENCES tx (ax, bx)
 ) ENGINE=InnoDB;
 ERROR HY000: Can't create table `test`.`t1` (errno: 150 "Foreign key constraint is incorrectly formed")
+CREATE TABLE t1 (
+a012345678901234567 int,
+b int,
+c0123456789012345678 int,
+FOREIGN KEY (a012345678901234567,c0123456789012345678,b) REFERENCES tx (x1,x2,x3)
+) ENGINE=InnoDB;
+ERROR HY000: Can't create table `test`.`t1` (errno: 150 "Foreign key constraint is incorrectly formed")

mysql-test/suite/innodb/t/innodb-fk.test

@@ -236,3 +236,11 @@ CREATE TABLE t1 (
     b char(255),
     FOREIGN KEY ( a012345678901234567890123456789012345678901, b ) REFERENCES tx (ax, bx)
 ) ENGINE=InnoDB;
+
+--error ER_CANT_CREATE_TABLE
+CREATE TABLE t1 (
+    a012345678901234567 int,
+    b int,
+    c0123456789012345678 int,
+    FOREIGN KEY (a012345678901234567,c0123456789012345678,b) REFERENCES tx (x1,x2,x3)
+) ENGINE=InnoDB;

storage/innobase/handler/ha_innodb.cc

@@ -12118,7 +12118,7 @@ class key_text
 					*(ptr++) = ' ';
 				}
 			} else {
-				ut_ad((size_t)(ptr - buf) < MAX_TEXT - 4);
+				ut_ad((size_t)(ptr - buf) <= MAX_TEXT - 4);
 				memcpy(ptr, "...", 3);
 				ptr += 3;
 				break;