Report errors if reading from a cache reader fails.

If we can't read the cached page, don't just return junk data.

Author: peadar

reader.cc

@@ -119,6 +119,8 @@ CacheReader::Page::load(const Reader &r, Off offset_)
 {
     assert(offset_ % data.size() == 0);
     len = r.read(offset_, data.size(), data.data());
+    if (len != data.size())
+       throw (Exception() << "failed to read page");
     offset = offset_;
 }
 
@@ -157,9 +159,9 @@ CacheReader::getPage(Off pageoff) const
     } else {
         p = std::make_unique<Page>();
     }
-     p->load(*upstream, pageoff);
-     pages.push_front(std::move(p));
-     return **pages.begin();
+    p->load(*upstream, pageoff);
+    pages.push_front(std::move(p));
+    return **pages.begin();
 }
 
 size_t