Fix a bug with the calculation of the remaining length

If the result of the string format was longer than the remaining length,
the returned remaining length would be negative, which would make very
strange things happen.

src/lager_format.erl

@@ -145,7 +145,7 @@ build([], Acc, MaxLen, _O) ->
 
 build2([{C,As,F,Ad,P,Pad,Enc}|Cs], Count, MaxLen) ->
     {S, Len} = control2(C, As, F, Ad, P, Pad, Enc, MaxLen div Count),
-    [S|build2(Cs, Count - 1, MaxLen - Len)];
+    [S|build2(Cs, Count - 1, MaxLen - abs(Len))];
 build2([C|Cs], Count, MaxLen) ->
     [C|build2(Cs, Count, MaxLen)];
 build2([], _, _) -> [].