fixes #24974; SIGSEGV when raising Defect/doAssert (#24985)

fixes #24974

requires `result` initializations when encountering unreachable code
(e.g. `quit`)

(cherry picked from commit 638a8bf84d)

tests/errmsgs/t24974.nim

@@ -0,0 +1,22 @@
+discard """
+  exitcode: 1
+  output: '''
+t24974.nim(22)           t24974
+t24974.nim(19)           d
+t24974.nim(16)           s
+assertions.nim(41)       failedAssertImpl
+assertions.nim(36)       raiseAssert
+fatal.nim(53)            sysFatal
+Error: unhandled exception: t24974.nim(16, 26) `false`  [AssertionDefect]
+'''
+"""
+
+
+type B = seq[array[1, byte]]
+proc s(_: var B): bool = doAssert false
+proc d(): B =
+  var k: B
+  if s(k): discard
+  quit 0
+  k
+for _ in [0]: discard d()