Fix ancient subroom location bug

Randomly placed subrooms were never generated touching
the right or bottom walls of the parent room.

This bug has been present since at least 3.1.0

dat/themerms.lua

@@ -197,7 +197,6 @@ themerooms = {
    end,
 
    -- Room in a room
-   -- FIXME: subroom location is too often left/top?
    function()
       des.room({ type = "ordinary", filled = 1,
                  contents = function()

doc/fixes3-7-0.txt

@@ -1092,6 +1092,8 @@ polymorphing into fire elemental allows you eat flammable items
 hitting sleeping monsters will cause them to wake up noisily
 demon gating happens more in Gehennom and less outside it
 intelligent peacefuls avoid digging shop or temple walls
+fix bug making random subrooms never touching the right or bottom
+	wall of the parent room
 
 
 Fixes to 3.7.0-x Problems that Were Exposed Via git Repository

src/sp_lev.c

@@ -1648,9 +1648,9 @@ create_subroom(
     if (h == -1)
         h = rnd(height - 3);
     if (x == -1)
-        x = rnd(width - w - 1) - 1;
+        x = rnd(width - w);
     if (y == -1)
-        y = rnd(height - h - 1) - 1;
+        y = rnd(height - h);
     if (x == 1)
         x = 0;
     if (y == 1)