Add some more miscellaneous asserts.

These clarify matters for static checkers (not to mention humans), and
seem inexpensive enough not to worry about adding.

settings.c

@@ -377,6 +377,7 @@ static void gprefs_from_str(const char *str,
      */
     while (n < nvals) {
         for (i = 0; i < nvals; i++) {
+	    assert(mapping[i].v >= 0);
 	    assert(mapping[i].v < 32);
 
 	    if (!(seen & (1 << mapping[i].v))) {

sshcrcda.c

@@ -149,6 +149,7 @@ bool detect_attack(
         for (i = HASH(c) & (ctx->n - 1); ctx->h[i] != HASH_UNUSED;
              i = (i + 1) & (ctx->n - 1)) {
             if (ctx->h[i] == HASH_IV) {
+                assert(IV); /* or we wouldn't have stored HASH_IV above */
                 if (!CMP(c, IV)) {
                     if (check_crc(c, buf, len, IV))
                         return true;      /* attack detected */

unix/gtkcols.c

@@ -2,6 +2,7 @@
  * gtkcols.c - implementation of the `Columns' GTK layout container.
  */
 
+#include <assert.h>
 #include <gtk/gtk.h>
 #include "defs.h"
 #include "gtkcompat.h"
@@ -662,6 +663,7 @@ static gint columns_compute_width(Columns *cols, widget_dim_fn_t get_width)
 
         childwidth = get_width(child);
 	colspan = child->colspan ? child->colspan : ncols-child->colstart;
+        assert(colspan > 0);
 
 #ifdef COLUMNS_WIDTH_DIAGNOSTICS
         printf("compute_width(%p): ", cols);

unix/gtkdlg.c

@@ -1850,8 +1850,9 @@ GtkWidget *layout_ctrls(struct dlgparam *dp, struct Shortcuts *scs,
     GtkWidget *ret;
     int i;
 
-    if (!s->boxname && s->boxtitle) {
+    if (!s->boxname) {
         /* This controlset is a panel title. */
+        assert(s->boxtitle);
         return gtk_label_new(s->boxtitle);
     }
 

unix/gtkfont.c

@@ -1614,6 +1614,7 @@ static void pangofont_draw_internal(unifont_drawctx *ctx, unifont *font,
         draw_layout = pango_cairo_draw_layout;
     }
 #endif
+    assert(draw_layout);
 
     if (wide)
 	cellwidth *= 2;