Fix GH-18107: Opcache CFG jmp optimization with try-finally breaks the exception table

If there's a try-finally where the try_op starts on a basic block with a
single JMP, and the JMP optimization causes that basic block to become
unreachable, then we update try_op.
In this case, there is no catch_op, so try_op is erroneously set to 0,
we should instead set it to `b->start`.

Author: nielsdos

Zend/Optimizer/zend_cfg.c

@@ -144,7 +144,7 @@ static void zend_mark_reachable_blocks(const zend_op_array *op_array, zend_cfg *
 							end = blocks + block_map[op_array->try_catch_array[j].finally_op];
 							while (b != end) {
 								if (b->flags & ZEND_BB_REACHABLE) {
-									op_array->try_catch_array[j].try_op = op_array->try_catch_array[j].catch_op;
+									op_array->try_catch_array[j].try_op = b->start;
 									changed = 1;
 									zend_mark_reachable(op_array->opcodes, cfg, blocks + block_map[op_array->try_catch_array[j].try_op]);
 									break;

ext/opcache/tests/opt/gh18107.phpt

@@ -0,0 +1,43 @@
+--TEST--
+GH-18107 (Opcache CFG jmp optimization with try-finally breaks the exception table)
+--EXTENSIONS--
+opcache
+--INI--
+opcache.optimization_level=0x10
+opcache.opt_debug_level=0x20000
+--FILE--
+<?php
+
+if (!isset($badvar)) {
+    throw new Exception("Should happen");
+}
+try {
+    while (true) { }
+} finally {
+    throw new Exception("Should not happen");
+}
+
+?>
+--EXPECTF--
+$_main:
+     ; (lines=%d, args=0, vars=%d, tmps=%d)
+     ; (after optimizer)
+     ; %s
+0000 T1 = ISSET_ISEMPTY_CV (isset) CV0($badvar)
+0001 JMPNZ T1 0006
+0002 V3 = NEW 1 string("Exception")
+0003 SEND_VAL_EX string("Should happen") 1
+0004 DO_FCALL
+0005 THROW V3
+0006 JMP 0006
+0007 V6 = NEW 1 string("Exception")
+0008 SEND_VAL_EX string("Should not happen") 1
+0009 DO_FCALL
+0010 THROW V6
+0011 FAST_RET T5
+EXCEPTION TABLE:
+     0006, -, 0007, 0011
+Fatal error: Uncaught Exception: Should happen in %s:%d
+Stack trace:
+#0 {main}
+  thrown in %s on line %d