pci: refuse empty ROM files

A zero size ROM file is invalid and should produce a warning.
Attempting to use a zero size file ends up hitting an assertion
qemu_ram_set_idstr() because RAMBlocks with duplicate addresses are
allocated - due to zero size the allocator doesn't increment the next
available RAMBlock offset.

Also convert __FUNCTION__ to __func__ while we're touching this code.
There are no other __FUNCTION__ instances in pci.c anymore.

Reported-by: Milos Ivanovic <milosivanovic@orcon.net.nz>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/pci/pci.c

@@ -1912,7 +1912,12 @@ static int pci_add_option_rom(PCIDevice *pdev, bool is_default_rom)
     size = get_image_size(path);
     if (size < 0) {
         error_report("%s: failed to find romfile \"%s\"",
-                     __FUNCTION__, pdev->romfile);
+                     __func__, pdev->romfile);
+        g_free(path);
+        return -1;
+    } else if (size == 0) {
+        error_report("%s: ignoring empty romfile \"%s\"",
+                     __func__, pdev->romfile);
         g_free(path);
         return -1;
     }