wasplib: add get_reachable_airpocket

builtin/client/wasplib.lua

@@ -843,6 +843,19 @@ function ws.inside_wall(pos)
     return false
 end
 
+function ws.find_closest_reachable_airpocket(pos)
+    local lp=ws.dircoord(0,0,0)
+    local nds=minetest.find_nodes_near(lp,5,{'air'})
+    local odst=10
+    local rt=lp
+    for k,v in ipairs(nds) do
+        local dst=vector.distance(pos,v)
+        if dst < odst then odst=dst rt=v end
+    end
+    if odst==10 then return false end
+    return vector.add(rt,vector.new(0,-1,0))
+end
+
 
 -- DEBUG
 local function printwieldedmeta()