runtime: replace some uses of newarray with newobject for maps

This avoids the never triggered capacity checks in newarray.

Change-Id: Ib72b204adcb9e3fd3ab963defe0cd40e22d5d492
Reviewed-on: https://go-review.googlesource.com/54731
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/runtime/hashmap.go

@@ -542,7 +542,7 @@ func mapassign(t *maptype, h *hmap, key unsafe.Pointer) unsafe.Pointer {
 	h.flags |= hashWriting
 
 	if h.buckets == nil {
-		h.buckets = newarray(t.bucket, 1)
+		h.buckets = newobject(t.bucket) // newarray(t.bucket, 1)
 	}
 
 again:

src/runtime/hashmap_fast.go

@@ -426,7 +426,7 @@ func mapassign_fast32(t *maptype, h *hmap, key uint32) unsafe.Pointer {
 	h.flags |= hashWriting
 
 	if h.buckets == nil {
-		h.buckets = newarray(t.bucket, 1)
+		h.buckets = newobject(t.bucket) // newarray(t.bucket, 1)
 	}
 
 again:
@@ -514,7 +514,7 @@ func mapassign_fast64(t *maptype, h *hmap, key uint64) unsafe.Pointer {
 	h.flags |= hashWriting
 
 	if h.buckets == nil {
-		h.buckets = newarray(t.bucket, 1)
+		h.buckets = newobject(t.bucket) // newarray(t.bucket, 1)
 	}
 
 again:
@@ -603,7 +603,7 @@ func mapassign_faststr(t *maptype, h *hmap, ky string) unsafe.Pointer {
 	h.flags |= hashWriting
 
 	if h.buckets == nil {
-		h.buckets = newarray(t.bucket, 1)
+		h.buckets = newobject(t.bucket) // newarray(t.bucket, 1)
 	}
 
 again: