Fix error in usr_str

library-asm/usr_str.asm

@@ -31,7 +31,7 @@ USR_STR:
 	and 11011111b ; Convert it to UPPER CASE
 	sub 144   ; CODE(UDG "A")
 	jr nc, CONT
-	adc a, 144   ; It was a letter
+	add a, 144   ; It was a letter
 	sub 'A'
 
     LOCAL CONT

tests/functional/fastcall0.asm

@@ -1192,7 +1192,7 @@ USR_STR:
 		and 11011111b ; Convert it to UPPER CASE
 		sub 144   ; CODE(UDG "A")
 		jr nc, CONT
-		adc a, 144   ; It was a letter
+		add a, 144   ; It was a letter
 		sub 'A'
 	    LOCAL CONT
 CONT:

tests/functional/spfill.asm

@@ -1192,7 +1192,7 @@ USR_STR:
 		and 11011111b ; Convert it to UPPER CASE
 		sub 144   ; CODE(UDG "A")
 		jr nc, CONT
-		adc a, 144   ; It was a letter
+		add a, 144   ; It was a letter
 		sub 'A'
 	    LOCAL CONT
 CONT:

tests/functional/usr0.asm

@@ -1398,7 +1398,7 @@ USR_STR:
 		and 11011111b ; Convert it to UPPER CASE
 		sub 144   ; CODE(UDG "A")
 		jr nc, CONT
-		adc a, 144   ; It was a letter
+		add a, 144   ; It was a letter
 		sub 'A'
 	    LOCAL CONT
 CONT:

tests/runtime/usr_str.bas

@@ -0,0 +1,7 @@
+
+PRINT USR "a"
+PRINT USR "A"
+PRINT USR "\a"
+PRINT USR "\A"
+
+