Fix potential buffer overflow

Signed-off-by: Slávek Banko <slavek.banko@axis.cz>
(cherry picked from commit 53090f7650)

kernel/kls_hdr/fmt_codec_hdr.cpp

@@ -283,7 +283,8 @@ bool fmt_codec::getHdrHead()
 	bool done = false;
 	s8 a, b;
 	s8 x[2], y[2];
-	s8 buff[80];
+	const u32 buffSize = 80;
+	s8 buff[buffSize];
 	u32 count = 0;
 
 	if(!frs.readK(hdr.sig, sizeof(hdr.sig)-1)) return false;
@@ -320,6 +321,9 @@ bool fmt_codec::getHdrHead()
 		if(!frs.readK(&a, sizeof(s8))) return false;
 
 		++count;
+		if (count > buffSize-1) {
+			return false;
+		}
 	}
 
 	buff[count] = '\0';