load_669: change songname type from 'signed char' to plain char.

Author: sezero

src/load_669.cpp

@@ -17,7 +17,7 @@
 typedef struct tagFILEHEADER669
 {
 	WORD sig;				// 'if' or 'JN'
-        signed char songmessage[108];	// Song Message
+	char songmessage[108];			// Song Message
 	BYTE samples;			// number of samples (1-64)
 	BYTE patterns;			// number of patterns (1-128)
 	BYTE restartpos;