Scan: Do not fail if a font dictionary lacks /FontInfo

This happens with SystemFont and SystemBoldFont on Xerox WC7845.

scan/scan

@@ -310,6 +310,7 @@ sub scan_psfonts() {
 	save exch
 	findfont
 	% Parse FontInfo and find version
+	dup /FontInfo known {
 		dup /FontInfo get
 			(%K% /Version) =
 			dup /Version known { dup /Version get == } {
@@ -318,6 +319,7 @@ sub scan_psfonts() {
 				} ifelse
 			} ifelse
 			pop
+	} { } ifelse
 	% Print Encoding
 	(%K% /Encoding) =
 	dup /Encoding known { dup /Encoding get == } { (???) == } ifelse