fix #1789 (binding to static params during generic proc sigmatch)

tests/generics/t1789.nim

@@ -0,0 +1,44 @@
+discard """
+  output: "3\n0"
+"""
+
+# https://github.com/Araq/Nim/issues/1789
+
+type
+  Foo[N: static[int]] = object
+
+proc bindStaticN[N](foo: Foo[N]) =
+  var ar0: array[3, int]
+  var ar1: array[N, int]
+  var ar2: array[1..N, int]
+  var ar3: array[0..(N+10), float]
+  echo N
+
+var f: Foo[3]
+f.bindStaticN
+
+# case 2
+
+type
+  ObjectWithStatic[X, Y: static[int], T] = object
+    bar: array[X * Y, T]   # this one works
+
+  AliasWithStatic[X, Y: static[int], T] = array[X * Y, T]
+
+var
+  x: ObjectWithStatic[1, 2, int]
+  y: AliasWithStatic[2, 3, int]
+
+# case 3
+
+type
+  Bar[N: static[int], T] = object
+    bar: array[N, T]
+
+proc `[]`*[N, T](f: Bar[N, T], n: range[0..(N - 1)]): T =
+  assert high(n) == N-1
+  result = f.bar[n]
+  
+var b: Bar[3, int]
+echo b[2]
+