Don't comment "; Next fragment/union" in .map files for empty section pieces

Fixes #1821

test/link/fragment-literals/a.asm

@@ -0,0 +1,18 @@
+section "PrintHL", rom0
+PrintHL::
+	; ...
+	ret
+
+section "PrintNth", rom0
+PrintNth::
+	ld hl, [[
+		dw [[ db "one\0" ]]
+		dw [[ db "two\0" ]]
+		dw [[ db "three\0" ]]
+		dw [[ db "four\0" ]]
+	]]
+	ld d, 0
+	ld e, a
+	add hl, de
+	add hl, de
+	call PrintHL

test/link/fragment-literals/ref.out.map

@@ -0,0 +1,10 @@
+SUMMARY:
+	ROM0: 39 bytes used / 16345 free
+
+ROM0 bank #0:
+	SECTION: $0000-$0025 ($0026 bytes) ["PrintNth"]
+	         $0000 = PrintNth
+	SECTION: $0026-$0026 ($0001 byte) ["PrintHL"]
+	         $0026 = PrintHL
+	EMPTY: $0027-$3fff ($3fd9 bytes)
+	TOTAL EMPTY: $3fd9 bytes

test/link/fragment-literals/ref.out.sym

@@ -0,0 +1,3 @@
+; File generated by rgblink
+00:0000 PrintNth
+00:0026 PrintHL

test/link/load-fragment/section-fragment/c.asm

@@ -1,8 +1,7 @@
 SECTION FRAGMENT "rom", ROM0
-Part3::
+; No labels in this fragment
 LOAD FRAGMENT "ram", WRAM0
 wPart3::
 	jr wPart1
 	jr wPart3
 ENDL
-Part3End::

test/link/load-fragment/section-fragment/ref.out.map

@@ -7,9 +7,6 @@ ROM0 bank #0:
 	         $0000 = Part1
 	         $0004 = Part1End
 	         ; Next fragment
-	         $0010 = Part3
-	         $0014 = Part3End
-	         ; Next fragment
 	         $0004 = Part2
 	         $0010 = Part2End
 	EMPTY: $0014-$3fff ($3fec bytes)

test/link/load-fragment/section-fragment/ref.out.sym

@@ -3,7 +3,5 @@
 00:0004 Part1End
 00:0004 Part2
 00:0010 Part2End
-00:0010 Part3
-00:0014 Part3End
 00:c000 wPart1
 00:c004 wPart3

test/link/test.sh

@@ -174,6 +174,16 @@ for test in fragment-align/*; do
 	evaluateTest
 done
 
+test="fragment-literals"
+startTest
+"$RGBASM" -o "$otemp" "$test"/a.asm
+continueTest
+rgblinkQuiet -o "$gbtemp" -m "$outtemp" -n "$outtemp2" "$otemp"
+tryCmpRom "$test"/ref.out.bin
+tryDiff "$test"/ref.out.map "$outtemp"
+tryDiff "$test"/ref.out.sym "$outtemp2"
+evaluateTest
+
 test="high-low"
 startTest
 "$RGBASM" -o "$otemp" "$test"/a.asm