ntdll: Don't crash on empty table in RtlAddFunctionTable().

dlls/ntdll/signal_x86_64.c

@@ -3458,7 +3458,7 @@ BOOLEAN CDECL RtlAddFunctionTable( RUNTIME_FUNCTION *table, DWORD count, DWORD64
         return FALSE;
 
     entry->base      = addr;
-    entry->end       = addr + table[count - 1].EndAddress;
+    entry->end       = addr + (count ? table[count - 1].EndAddress : 0);
     entry->table     = table;
     entry->count     = count;
     entry->max_count = 0;

dlls/ntdll/tests/exception.c

@@ -2103,6 +2103,14 @@ static void test_dynamic_unwind(void)
     ok( !pRtlDeleteFunctionTable( runtime_func ),
         "RtlDeleteFunctionTable returned success for nonexistent table runtime_func = %p\n", runtime_func );
 
+    /* Empty table */
+    ok( pRtlAddFunctionTable( runtime_func, 0, (ULONG_PTR)code_mem ),
+        "RtlAddFunctionTable failed for empty table\n" );
+    ok( pRtlDeleteFunctionTable( runtime_func ),
+        "RtlDeleteFunctionTable failed for empty table\n" );
+    ok( !pRtlDeleteFunctionTable( runtime_func ),
+        "RtlDeleteFunctionTable succeeded twice for empty table\n" );
+
     /* Test RtlInstallFunctionTableCallback with both low bits unset */
     table = (ULONG_PTR)code_mem;
     ok( !pRtlInstallFunctionTableCallback( table, (ULONG_PTR)code_mem, code_offset + 32, &dynamic_unwind_callback, (PVOID*)&count, NULL ),