Recalc mon-hits-you distance variables

When a monster could first knock you back and then grab you,
the game would emit impossible, because the knockback moved you
but the distance variables used for the grab attack were not
updated.

Update the range variables within the loop iterating through
the monster attacks.

src/mhitu.c

@@ -11,6 +11,8 @@ static NEARDATA struct obj *mon_currwep = (struct obj *) 0;
 static void missmu(struct monst *, boolean, struct attack *);
 static void mswings(struct monst *, struct obj *, boolean);
 static void wildmiss(struct monst *, struct attack *);
+static void calc_mattacku_vars(struct monst *, boolean *, boolean *,
+                               boolean *, boolean *);
 static void summonmu(struct monst *, boolean);
 static int hitmu(struct monst *, struct attack *);
 static int gulpmu(struct monst *, struct attack *);
@@ -378,6 +380,18 @@ getmattk(struct monst *magr, struct monst *mdef,
     return attk;
 }
 
+/* calc some variables needed for mattacku() */
+static void
+calc_mattacku_vars(struct monst *mtmp,
+                   boolean *ranged, boolean *range2,
+                   boolean *foundyou, boolean *youseeit)
+{
+    *ranged = (mdistu(mtmp) > 3);
+    *range2 = !monnear(mtmp, mtmp->mux, mtmp->muy);
+    *foundyou = u_at(mtmp->mux, mtmp->muy);
+    *youseeit = canseemon(mtmp);
+}
+
 /*
  * mattacku: monster attacks you
  *      returns 1 if monster dies (e.g. "yellow light"), 0 otherwise
@@ -404,12 +418,11 @@ mattacku(register struct monst *mtmp)
      *     excessively verbose miss feedback when monster can do multiple
      *     attacks and would miss the same wrong spot each time.)
      */
-    boolean ranged = (mdistu(mtmp) > 3),
-            range2 = !monnear(mtmp, mtmp->mux, mtmp->muy),
-            foundyou = u_at(mtmp->mux, mtmp->muy),
-            youseeit = canseemon(mtmp),
+    boolean ranged, range2, foundyou, youseeit,
             skipnonmagc = FALSE;
 
+    calc_mattacku_vars(mtmp, &ranged, &range2, &foundyou, &youseeit);
+
     if (!ranged)
         nomul(0);
     if (DEADMONSTER(mtmp) || (Underwater && !is_swimmer(mtmp->data)))
@@ -652,6 +665,8 @@ mattacku(register struct monst *mtmp)
     gs.skipdrin = FALSE; /* [see mattackm(mhitm.c)] */
 
     for (i = 0; i < NATTK; i++) {
+        /* recalc in case attack moved hero */
+        calc_mattacku_vars(mtmp, &ranged, &range2, &foundyou, &youseeit);
         sum[i] = MM_MISS;
         if (i > 0 && foundyou /* previous attack might have moved hero */
             && (mtmp->mux != u.ux || mtmp->muy != u.uy))