Fix RGBLINK ignoring alignment constraints when placing empty sections

Fixes #2095

test/link/zero-byte-sect-constraints.asm

@@ -0,0 +1,23 @@
+; Sections going into space already reserved.
+SECTION "address", ROM0[$0135]
+	assert @ == $0135
+
+SECTION "align16", ROM0, ALIGN[16,$0123] ; Should be equivalent to the above.
+	assert @ == $0123
+
+SECTION "align", ROM0, ALIGN[8,42]
+	assert @ == 42 ; Assuming that it goes into the first suitable location.
+
+
+SECTION "om nom nom", ROM0[0]
+	ds $200 ; Filling the first part of ROM0, so that the above don't land in a “free space” block but the next do.
+
+
+SECTION "free address", ROM0[$2468]
+	assert @ == $2468
+
+SECTION "free align16", ROM0, ALIGN[16,$2222] ; Should be equivalent to the above.
+	assert @ == $2222
+
+SECTION "free align", ROM0, ALIGN[13,$1234] ; Has more than one suitable location, so cannot be trivially solved.
+	assert @ == $1234 ; Assuming that it goes into the first suitable location.