Fix #80002: calc free space for new interned string is wrong

We need to calculate the free size in bytes.

Patch contributed by t-matsuno.

Closes GH-6024

Author: cmb69

NEWS

@@ -6,6 +6,10 @@ PHP                                                                        NEWS
   . Fixed bug #80007 (Potential type confusion in unixtojd() parameter parsing).
     (Andy Postnikov)
 
+- OPcache:
+  . Fixed bug #80002 (calc free space for new interned string is wrong).
+    (t-matsuno)
+
 03 Sep 2020, PHP 7.3.22
 
 - Core:

ext/opcache/ZendAccelerator.c

@@ -487,7 +487,7 @@ zend_string* ZEND_FASTCALL accel_new_interned_string(zend_string *str)
 		} while (pos != STRTAB_INVALID_POS);
 	}
 
-	if (UNEXPECTED(ZCSG(interned_strings).end - ZCSG(interned_strings).top < STRTAB_STR_SIZE(str))) {
+	if (UNEXPECTED((char*)ZCSG(interned_strings).end - (char*)ZCSG(interned_strings).top < STRTAB_STR_SIZE(str))) {
 	    /* no memory, return the same non-interned string */
 		zend_accel_error(ACCEL_LOG_WARNING, "Interned string buffer overflow");
 		return str;