Don't read unlimited data from files

It now guards against reading infinite files such as `/dev/zero`.
And most readings are bound with a (lax) limit.
As a side effect, more checking are done when reading a file and
overall the reading procedure is more robust.

PR #19095.

test/CMakeLists.txt

@@ -17,6 +17,7 @@ set(testFiles
     testutilscompare.cpp
     testutilsbytearray.cpp
     testutilsgzip.cpp
+    testutilsio.cpp
     testutilsstring.cpp
     testutilsversion.cpp
 )