fix(profiler): restore signal depth after longjmp unwinds segvHandler

longjmp() in checkFault() bypasses C++ destructors, leaving
_in_signal_handler_depth stuck at an inflated value after crash recovery.
When SIGSEGV fires inside walkVM (depth=1 from SIGPROF handler), segvHandler
increments depth to 2, then longjmp unwinds back to setjmp in walkVM
without running SignalHandlerScope::~SignalHandlerScope(). Explicitly
decrement depth at the longjmp recovery site to undo the skipped destructor.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

Author: jbachorik

ddprof-lib/src/main/cpp/hotspot/hotspotSupport.cpp

@@ -13,6 +13,7 @@
 #include "hotspot/vmStructs.inline.h"
 #include "jvmSupport.h"
 #include "profiler.h"
+#include "signalSafety.h"
 #include "stackWalker.inline.h"
 #include "frames.h"
 
@@ -187,6 +188,11 @@ __attribute__((no_sanitize("address"))) int HotspotSupport::walkVM(void* ucontex
             profiled_thread->setCrashProtectionActive(true);
         }
         if (setjmp(crash_protection_ctx) != 0) {
+            // longjmp from segvHandler bypasses its SignalHandlerScope destructor,
+            // leaving _in_signal_handler_depth inflated by one.  Undo that here.
+            if (_in_signal_handler_depth > 0) {
+                --_in_signal_handler_depth;
+            }
             if (profiled_thread != nullptr) {
                 profiled_thread->setCrashProtectionActive(false);
             }