Fix version 1 arc header reading

The code for v1 hdr reading was reading the packed header directly into an
unpacked struct.

Use the same read to dummy array, then manual unpack to header struct as
used for v2 headers for v1 headers too.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
diff -ur arc-5.21p/arcio.c arc-5.21p.new/arcio.c
--- arc-5.21p/arcio.c	2010-08-07 15:06:42.000000000 +0200
+++ arc-5.21p.new/arcio.c	2015-01-16 12:59:43.203289118 +0100
@@ -37,6 +37,7 @@
 #endif
 	char            name[FNLEN];	/* filename buffer */
 	int             try = 0;/* retry counter */
+	int             hdrlen;
 	static int      first = 1;	/* true only on first read */
 
 	if (!f)			/* if archive didn't open */
@@ -92,23 +93,19 @@
 		printf("I think you need a newer version of ARC.\n");
 		exit(1);
 	}
+
 	/* amount to read depends on header type */
+	if (hdrver == 1) {
+		hdrlen = 23; /* old style is shorter */
+	} else {
+		hdrlen = 27;
+	}
 
-	if (hdrver == 1) {	/* old style is shorter */
-		if (fread(hdr, sizeof(struct heads) - sizeof(long int), 1, f) != 1)
-			arcdie("%s was truncated", arcname);
-		hdrver = 2;	/* convert header to new format */
-		hdr->length = hdr->size;	/* size is same when not
-						 * packed */
-	} else
-#if	MSDOS
-		if (fread(hdr, sizeof(struct heads), 1, f) != 1)
-			arcdie("%s was truncated", arcname);
-#else
-		if (fread(dummy, 27, 1, f) != 1)
-			arcdie("%s was truncated", arcname);
+	if (fread(dummy, hdrlen, 1, f) != 1)
+		arcdie("%s was truncated", arcname);
 
 	for (i = 0; i < FNLEN; hdr->name[i] = dummy[i], i++);
+	hdr->name[FNLEN - 1] = 0; /* ensure 0 termination */
 #if	_MTS
 	(void) atoe(hdr->name, strlen(hdr->name));
 #endif
@@ -116,8 +113,14 @@
 	hdr->date = (short) ((dummy[18] << 8) + dummy[17]);
 	hdr->time = (short) ((dummy[20] << 8) + dummy[19]);
 	hdr->crc = (short) ((dummy[22] << 8) + dummy[21]);
-	for (i = 0, hdr->length=0; i<4; hdr->length<<=8, hdr->length += dummy[26-i], i++);
-#endif
+
+	if (hdrver == 1) {
+		hdrver = 2;	/* convert header to new format */
+		hdr->length = hdr->size;	/* size is same when not
+						 * packed */
+	} else {
+		for (i = 0, hdr->length=0; i<4; hdr->length<<=8, hdr->length += dummy[26-i], i++);
+	}
 
 	if (hdr->date > olddate
 	    || (hdr->date == olddate && hdr->time > oldtime)) {