Blessed potion of see invisible

Blessed potion of see invisible was guaranteed to give see invisible
intrinsic, making it far too easy to acquire.  It now has 1/10 chance
of giving it permanently, somewhat similarly to potion of invisibility.

doc/fixes3-7-0.txt

@@ -1593,6 +1593,7 @@ hero has a small chance of catching items thrown at them
 wizard mode: history menu for #wizwish and WIZKIT
 monster priests and wizards did not cast spells
 prevent phaseable monsters hiding deep inside nondiggable walls
+blessed potion of see invisible does not guarantee the intrinsic
 
 
 Fixes to 3.7.0-x General Problems Exposed Via git Repository

src/potion.c

@@ -863,7 +863,7 @@ peffect_see_invisible(struct obj *otmp)
          */
         make_blinded(0L, TRUE);
     }
-    if (otmp->blessed)
+    if (otmp->blessed && !rn2(10))
         HSee_invisible |= FROMOUTSIDE;
     else
         incr_itimeout(&HSee_invisible, rn1(100, 750));