Fix uninitialized read in m-tx grep func

[Raphael Isemann]

The m-tx `grep` function reads uninitialized stack memory. This patch
just sets the initial value to 1 which allows the while statement that
uses it uninitialized to run as before. See the annotated source code
below for where the bug is:

```
void grep(Char *source_, Char *pattern_, Char *target)
{
 struct LOC_grep V;
 [...]
 // NOTE: All members aside from 'matching' initialized.
 V.source = source_;
 V.pattern = pattern_;
 V.index = 0;
 V.s = 1;
 V.p = 1;
 for (V.i = 0; V.i <= 9; V.i++) {
   V.p1[V.i] = 1;
   V.p2[V.i] = 0;
 }
 // NOTE: vvvvvvvv use of uninitialized member 'matching'.
 while (V.matching && V.p <= strlen(V.pattern) && V.s <= strlen(V.source))
```

Note that the upstream m-tx repository seems to be written in pascal
but the problematic version in texlive is (auto translated?) C. That's
why I sent the patch here. Thanks!

- Raphael Isemann
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