Preserve \@ through INCLUDE

Fixes #1112

src/asm/fstack.c

@@ -351,8 +351,10 @@ void fstk_RunInclude(char const *path)
 	if (!contextStack->lexerState)
 		fatalerror("Failed to set up lexer for file include\n");
 	lexer_SetStateAtEOL(contextStack->lexerState);
-	// We're back at top-level, so most things are reset
-	contextStack->uniqueID = macro_UndefUniqueID();
+	// We're back at top-level, so most things are reset,
+	// but not the unique ID, since INCLUDE may be inside a
+	// MACRO or REPT/FOR loop
+	contextStack->uniqueID = contextStack->parent->uniqueID;
 }
 
 // Similar to `fstk_RunInclude`, but not subject to `-MG`, and

test/asm/include-unique-id.asm

@@ -0,0 +1,24 @@
+MACRO mac
+	println "outer mac: \@ (\#)"
+	INCLUDE "include-unique-id.inc"
+ENDM
+
+	DEF state = 1
+	mac hello, world
+	mac goodbye, world
+
+REPT 2
+	DEF state = 2
+	println "outer rept before: \@"
+	INCLUDE "include-unique-id.inc"
+
+	FOR n, 3
+		DEF state = 3
+		println "outer for: \@ ({n})"
+		INCLUDE "include-unique-id.inc"
+	ENDR
+
+	DEF state = 4
+	println "outer rept after: \@"
+	INCLUDE "include-unique-id.inc"
+ENDR

test/asm/include-unique-id.inc

@@ -0,0 +1,9 @@
+IF state == 1
+	println "inner mac: \@ (\#)"
+ELIF state == 2
+	println "inner rept before: \@"
+ELIF state == 3
+	println "inner for: \@ ({n})"
+ELIF state == 4
+	println "inner rept after: \@"
+ENDC

test/asm/include-unique-id.out

@@ -0,0 +1,24 @@
+outer mac: _u1 (hello,world)
+inner mac: _u1 (hello,world)
+outer mac: _u2 (goodbye,world)
+inner mac: _u2 (goodbye,world)
+outer rept before: _u3
+inner rept before: _u3
+outer for: _u4 ($0)
+inner for: _u4 ($0)
+outer for: _u5 ($1)
+inner for: _u5 ($1)
+outer for: _u6 ($2)
+inner for: _u6 ($2)
+outer rept after: _u3
+inner rept after: _u3
+outer rept before: _u7
+inner rept before: _u7
+outer for: _u8 ($0)
+inner for: _u8 ($0)
+outer for: _u9 ($1)
+inner for: _u9 ($1)
+outer for: _u10 ($2)
+inner for: _u10 ($2)
+outer rept after: _u7
+inner rept after: _u7