Return t from completion-emacs22-try-completion only for completions

Return t from completion-emacs22-try-completion only for completions

The emacs22 completion style ignores the text after point when
computing completions.  However, it still needs to take into account
the entire string it's given, to avoid returning incorrect values.

Previously, completion-emacs22-try-completion would return t if the
text before point was an exact completion.  But this is effectively
saying that the entire input string was an exact completion, which may
not be correct.  This would cause completing-read with REQUIRE-MATCH=t
to return a non-completion.

Now, completion-emacs22-try-completion only returns t if the entire
input string is an exact completion.

* lisp/minibuffer.el (completion-emacs22-try-completion): Return t
only if the entire input string is an exact completion.  (Bug#67210)