Bug 21729 – rawRead derefences null pointer if invoked on closed File (segfault)

```n.d import std.stdio; void main () { File f; ubyte [1] u; auto n = f.rawRead (u); } ``` $ dmd -g n.d $ gdb ./n [...] (gdb) r [...] Program received signal SIGSEGV, Segmentation fault. 0xXXXXXXXXXXXXXXXX in std.stdio.File() (this=..., buffer=...) at [...]/dmd2/linux/bin64/../../src/phobos/std/stdio.d:1036 1036 immutable freadResult = trustedFread(_p.handle, buffer); (gdb) p _p $1 = (struct std.stdio.File.Impl *) 0x0

I think, before doing this "trustedFread" in (currently) line 1057, there needs to be an `enforce(_p !is null, some message)`. But I'm not firm enough in std.stdio, so I don't want to file a fixing PR. Might fix 21728 too.

@berni44 created dlang/phobos pull request #8025 "Fix Issues 21728, 21729 and 21730 (check for open file, before using trustedFread)" fixing this issue: - Fix Issue 21729 - rawRead derefences null pointer if invoked on closed File (segfault) https://github.com/dlang/phobos/pull/8025

dlang/phobos pull request #8025 "Fix Issues 21728, 21729 and 21730 (check for open file, before using trustedFread)" was merged into stable: - 3b501e1ddca1b144234a0fa27d6dc7109b7c9aa7 by berni44: Fix Issue 21729 - rawRead derefences null pointer if invoked on closed File (segfault) https://github.com/dlang/phobos/pull/8025