util: check for error after reading from a file

`fread(3)` does not distinguish between end-of-file and error,
and callers must use `feof(3)` and `ferror(3)` to determine which
occurred.

src/streams.cpp

@@ -4,6 +4,8 @@
 
 #include <span.h>
 #include <streams.h>
+#include <tinyformat.h>
+#include <util/syserror.h>
 
 #include <array>
 
@@ -23,8 +25,9 @@ std::size_t AutoFile::detail_fread(Span<std::byte> dst)
 
 void AutoFile::read(Span<std::byte> dst)
 {
-    if (detail_fread(dst) != dst.size()) {
-        throw std::ios_base::failure(feof() ? "AutoFile::read: end of file" : "AutoFile::read: fread failed");
+    if (detail_fread(dst) != dst.size() || ferror(m_file)) {
+        throw std::ios_base::failure(feof() ? "AutoFile::read: end of file" :
+                                              strprintf("AutoFile::read: error: %s", SysErrorString(errno)));
     }
 }