"Find definition" sometimes fails from core executable in some on 2.2.10

[Pierre Neidhardt]

This is a bit of an odd one because I don't have a good recipe to share.

When I dump a core executable which includes a specific package `ambrevar/shell`, then load the said core executable and input the following

```
(SB-INTROSPECT:FIND-DEFINITION-SOURCES-BY-NAME 'AMBREVAR/SHELL:FILE->STRING :FUNCTION)
```

it fails with

```
  Invalid index 8 for (SIMPLE-ARRAY (UNSIGNED-BYTE 16)
                       (7)) , should be a non-negative integer below 7.

Backtrace for: #<SB-THREAD:THREAD "main thread" RUNNING {10038A8003}>
0: (SB-DEBUG::DEBUGGER-DISABLED-HOOK #<SB-KERNEL:INDEX-TOO-LARGE-ERROR expected-type: (INTEGER 0 6) datum: 8> #<unused argument> :QUIT T)
1: (SB-DEBUG::RUN-HOOK *INVOKE-DEBUGGER-HOOK* #<SB-KERNEL:INDEX-TOO-LARGE-ERROR expected-type: (INTEGER 0 6) datum: 8>)
2: (INVOKE-DEBUGGER #<SB-KERNEL:INDEX-TOO-LARGE-ERROR expected-type: (INTEGER 0 6) datum: 8>)
3: (ERROR SB-KERNEL:INDEX-TOO-LARGE-ERROR :DATUM 8 :SEQUENCE #(0 336 364 580 603 1338 1360) :EXPECTED-TYPE (INTEGER 0 6))
4: (ELT #(0 336 364 580 603 1338 1360) 8)
5: (SB-INTROSPECT::FIND-FUNCTION-DEFINITION-SOURCE #<FUNCTION AMBREVAR/SHELL:FILE->STRING>)
6: (SB-INTROSPECT:FIND-DEFINITION-SOURCES-BY-NAME AMBREVAR/SHELL:FILE->STRING :FUNCTION)
7: (SB-INT:SIMPLE-EVAL-IN-LEXENV (SB-INTROSPECT:FIND-DEFINITION-SOURCES-BY-NAME (QUOTE AMBREVAR/SHELL:FILE->STRING) :FUNCTION) #<NULL-LEXENV>)
8: (EVAL (SB-INTROSPECT:FIND-DEFINITION-SOURCES-BY-NAME (QUOTE AMBREVAR/SHELL:FILE->STRING) :FUNCTION))
9: (INTERACTIVE-EVAL (SB-INTROSPECT:FIND-DEFINITION-SOURCES-BY-NAME (QUOTE AMBREVAR/SHELL:FILE->STRING) :FUNCTION) :EVAL NIL)
10: (SB-IMPL::REPL-FUN NIL)
11: ((LAMBDA NIL :IN SB-IMPL::TOPLEVEL-REPL))
12: (SB-IMPL::%WITH-REBOUND-IO-SYNTAX #<FUNCTION (LAMBDA NIL :IN SB-IMPL::TOPLEVEL-REPL) {1003CB969B}>)
13: (SB-IMPL::TOPLEVEL-REPL NIL)
14: (SB-IMPL::TOPLEVEL-INIT)
15: ((FLET SB-UNIX::BODY :IN SB-IMPL::START-LISP))
16: ((FLET "WITHOUT-INTERRUPTS-BODY-3" :IN SB-IMPL::START-LISP))
17: (SB-IMPL::%START-LISP)

```

It works for symbols exported before this one in the file, but all symbols exported after this s-exp index 8 fail in a similar fashion. It's as if the source definition information was recorded shorted than it really is when dumping the image.

If I reload the system it works again.
Other packages (as far as I've tried) don't suffer from this issue, which makes this a bit hard to reproduce.

The problem did not occur on SBCL 2.2.6.