Fix captures beginning in expansions

Fixes #590

src/asm/lexer.c

@@ -1962,13 +1962,11 @@ restart:
 
 static char *startCapture(void)
 {
-	assert(!lexerState->expansions);
-
 	lexerState->capturing = true;
 	lexerState->captureSize = 0;
 	lexerState->disableMacroArgs = true;
 
-	if (lexerState->isMmapped) {
+	if (lexerState->isMmapped && !lexerState->expansions) {
 		return &lexerState->ptr[lexerState->offset];
 	} else {
 		lexerState->captureCapacity = 128; /* The initial size will be twice that */

test/asm/equs-macrodef.asm

@@ -0,0 +1,3 @@
+DEFINE equs "mac: MACRO\nPRINTT \"Hello :D\\n\"\nENDM"
+DEFINE
+	mac

test/asm/equs-macrodef.out

@@ -0,0 +1 @@
+Hello :D