Do not try to read empty files.

CI report [1].

  [1]: https://clickhouse-test-reports.s3.yandex.net/30190/fe534553b2a0ac543795956b3fbde673cf5a342b/functional_stateless_tests_(debug).html#fail1

Fixes: 01560_ttl_remove_empty_parts in debug build (and some other tests)
v0: fix MergeTreeDataPartCompact::loadIndexGranularity()/MergeTreeDataPartWide::loadIndexGranularity()
v2: use EmptyReadBuffer in DiskLocal::readFile()
v3: introduce ReadBufferFromEmptyFile
v4: rebase against readbuffer-real-size branch

src/IO/ReadBufferFromEmptyFile.h

@@ -0,0 +1,23 @@
+#pragma once
+
+#include <IO/ReadBuffer.h>
+
+namespace DB
+{
+
+/// In case of empty file it does not make any sense to read it.
+///
+/// Plus regular readers from file has an assert that buffer is not empty, that will fail:
+/// - ReadBufferFromFileDescriptor
+/// - SynchronousReader
+/// - ThreadPoolReader
+class ReadBufferFromEmptyFile : public ReadBufferFromFileBase
+{
+private:
+    bool nextImpl() override { return false; }
+    std::string getFileName() const override { return "<empty>"; }
+    off_t seek(off_t /*off*/, int /*whence*/) override { return 0; }
+    off_t getPosition() override { return 0; }
+};
+
+}

src/IO/createReadBufferFromFileBase.cpp

@@ -1,4 +1,5 @@
 #include <IO/createReadBufferFromFileBase.h>
+#include <IO/ReadBufferFromEmptyFile.h>
 #include <IO/ReadBufferFromFile.h>
 #include <IO/MMapReadBufferFromFileWithCache.h>
 #include <IO/AsynchronousReadBufferFromFile.h>
@@ -33,6 +34,8 @@ std::unique_ptr<ReadBufferFromFileBase> createReadBufferFromFileBase(
     char * existing_memory,
     size_t alignment)
 {
+    if (size.has_value() && !*size)
+        return std::make_unique<ReadBufferFromEmptyFile>();
     size_t estimated_size = size.has_value() ? *size : 0;
 
     if (!existing_memory