exec: fix error handling in file_ram_alloc

One instance of double closing, and invalid close(-1) in some cases
of "goto error".
Reviewed-by: NLaszlo Ersek <lersek@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

exec.c

@@ -1239,7 +1239,7 @@ static void *file_ram_alloc(RAMBlock *block,
     char *sanitized_name;
     char *c;
     void *area;
-    int fd;
+    int fd = -1;
     int64_t page_size;
 
     if (kvm_enabled() && !kvm_has_sync_mmu()) {
@@ -1321,7 +1321,6 @@ static void *file_ram_alloc(RAMBlock *block,
     if (area == MAP_FAILED) {
         error_setg_errno(errp, errno,
                          "unable to map backing store for guest RAM");
-        close(fd);
         goto error;
     }
 
@@ -1336,7 +1335,9 @@ error:
     if (unlink_on_error) {
         unlink(path);
     }
-    close(fd);
+    if (fd != -1) {
+        close(fd);
+    }
     return NULL;
 }
 #endif