engine: Space offers the reading in Katakana last; 0 always commits the reading

Every Japanese IME converts a reading to Katakana on demand; strans made
the user switch to the Katakana mode and type again.  Space now adds
the reading in Katakana after the dictionary candidates, so a loanword
the dictionary lacks converts with one Space and Enter, and 漢字 users
still get 漢字 first.

0 committed the reading only while candidates showed; without them it
typed a 0 as well.  It now commits any Japanese reading, the counterpart
of 1-9 picking candidates, as the README always said.

strans.c

@@ -313,6 +313,23 @@ dictqjp(void)
 	dictqokuri(&reading);
 }
 
+/* The reading in Katakana is the last candidate, as in every IME. */
+static void
+katakouho(void)
+{
+	Str reading, k;
+	int i;
+
+	if(!jpreading(im.l->map, &im.pre, &im.raw, &reading))
+		return;
+	k = reading;
+	for(i = 0; i < k.n; i++)
+		if(k.r[i] >= L'ぁ' && k.r[i] <= L'ゖ')
+			k.r[i] += L'ァ' - L'ぁ';
+	if(scmp(&k, &reading) != 0)
+		addkouho(&k);
+}
+
 static int
 setlang(int c)
 {
@@ -755,8 +772,9 @@ transition(u32int ks, u32int mod, Str *com)
 		return 1;
 	}
 	if(ks == ' ' && isjp(&im) && haspre(&im) && !(mod & ~Mshift)){
-		/* Space converts: it steps through the candidates, or
-		 * commits a reading that has none. */
+		/* Space converts: it steps through the candidates, Katakana
+		 * last; a reading with none is committed. */
+		katakouho();
 		if(im.nkouho != 0)
 			cyclekouho(mod & Mshift ? -1 : 1);
 		else
@@ -811,8 +829,8 @@ transition(u32int ks, u32int mod, Str *com)
 		flush(com);
 		return setlang(c);
 	}
-	if(ks == '0' && im.nkouho > 0){
-		im.sel = -1;
+	if(ks == '0' && isjp(&im) && haspre(&im)){
+		im.sel = -1;	/* 0 commits the reading, as 1-9 pick candidates */
 		flush(com);
 		return 1;
 	}