SuperSize: Caspian: Don't crash on empty component list

Sparse .sizediffs may have zero symbols, and so zero components.

Change-Id: I8d24f5715c6b82ea38b544ffa4a8aaad5b988b69
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1945275Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Jasper Chapman-Black <jaspercb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#720672}

tools/binary_size/libsupersize/caspian/file_format.cc

@@ -262,8 +262,8 @@ void ParseSizeInfo(const char* gzipped, unsigned long len, SizeInfo* info) {
   if (has_components) {
     // List of component names
     int n_components = ReadLoneInt(&rest);
-    if (n_components <= 0) {
-      std::cerr << "Unexpected non-positive components list length: "
+    if (n_components < 0) {
+      std::cerr << "Unexpected negative components list length: "
                 << n_components << std::endl;
       exit(1);
     }