Provide insertion failure reasons from only eligible pockets

When trying to insert "plastic painkiller bottle" into a full backpack,
the failure reason was previously shown as "item is too short". This
commit instead makes the failure reason only show from pockets that
could possibly contain the item.

In effect, the failure reason when inserting "plastic painkiller bottle"
into a full backpack will now instead be "not enough space".

src/item_contents.cpp

@@ -1109,6 +1109,7 @@ ret_val<void> item_contents::can_contain( const item &it, int &copies_remaining,
         units::volume remaining_parent_volume ) const
 {
     ret_val<void> ret = ret_val<void>::make_failure( _( "is not a container" ) );
+    bool has_ret = false;
 
     if( copies_remaining <= 0 ) {
         return ret_val<void>::make_success();
@@ -1139,7 +1140,15 @@ ret_val<void> item_contents::can_contain( const item &it, int &copies_remaining,
         if( copies_remaining <= 0 ) {
             return ret_val<void>::make_success();
         }
+        int n = copies_remaining;
+        bool could_contain = pocket.can_contain( it, n, /*ignore_contents=*/true ).success();
+        if( has_ret && !could_contain ) {
+            // This pocket could never contain the item, even if the pocket was emptied.
+            // So we would prefer to get the failure msg from another pocket which could potentially hold the item.
+            continue;
+        }
         ret = ret_val<void>::make_failure( pocket_contain_code.str() );
+        has_ret = true;
     }
     return ret;
 }