static-delta: Handle LZMA_BUF_ERROR returned by zlib

zlib can return LZMA_BUF_ERROR, which indicates that either
the input or output buffer has size zero. This case should cause
the correct error to be passed back from g_converter_convert
to expand the relevant buffer. Since this error is ambiguous
as to which buffer is too small, an explicit check on the
output buffer size is added as well.

https://bugzilla.gnome.org/show_bug.cgi?id=756260

src/libostree/ostree-lzma-common.c

@@ -62,6 +62,10 @@ _ostree_lzma_return (lzma_ret   res,
       g_set_error_literal (error, G_IO_ERROR, G_IO_ERROR_FAILED,
 			   "Data is corrupt");
       return G_CONVERTER_ERROR;
+    case LZMA_BUF_ERROR:
+      g_set_error_literal (error, G_IO_ERROR, G_IO_ERROR_PARTIAL_INPUT,
+         "Input buffer too small");
+      return G_CONVERTER_ERROR;
     default:
       g_set_error_literal (error, G_IO_ERROR, G_IO_ERROR_FAILED,
 			   "Unrecognized LZMA error");

src/libostree/ostree-lzma-compressor.c

@@ -173,6 +173,13 @@ _ostree_lzma_compressor_convert (GConverter *converter,
   int res;
   lzma_action action; 
 
+  if (inbuf_size != 0 && outbuf_size == 0)
+    {
+      g_set_error_literal (error, G_IO_ERROR, G_IO_ERROR_NO_SPACE,
+         "Output buffer too small");
+      return G_CONVERTER_ERROR;
+    }
+
   if (!self->initialized)
     {
       res = lzma_easy_encoder (&self->lstream, 8, LZMA_CHECK_CRC64);

src/libostree/ostree-lzma-decompressor.c

@@ -104,6 +104,13 @@ _ostree_lzma_decompressor_convert (GConverter *converter,
   OstreeLzmaDecompressor *self = OSTREE_LZMA_DECOMPRESSOR (converter);
   int res;
 
+  if (inbuf_size != 0 && outbuf_size == 0)
+    {
+      g_set_error_literal (error, G_IO_ERROR, G_IO_ERROR_NO_SPACE,
+         "Output buffer too small");
+      return G_CONVERTER_ERROR;
+    }
+
   if (!self->initialized)
     {
       res = lzma_stream_decoder (&self->lstream, G_MAXUINT64, 0);