FIX: crash when composing large block

fixes: Oldes/Rebol-issues#1906

Author: Oldes

src/core/c-do.c

@@ -1317,10 +1317,14 @@ x*/	static REBINT Do_Args_Light(REBVAL *func, REBVAL *path, REBSER *block, REBCN
 **
 ***********************************************************************/
 {
-	REBVAL *value;
+	REBVAL *value = VAL_BLK_DATA(block);
 	REBINT start = DSP + 1;
+	
+	if (start + VAL_LEN(block) + 100 > SERIES_REST(DS_Series)) {
+		Expand_Stack(VAL_LEN(block));
+	}
 
-	for (value = VAL_BLK_DATA(block); NOT_END(value); value++) {
+	for (; NOT_END(value); value++) {
 		if (IS_PAREN(value)) {
 			// Eval the paren, and leave result on the stack:
 			DO_BLK(value);

src/tests/units/crash-test.r3

@@ -151,6 +151,11 @@ Rebol [
 	--assert #0102030405060708090A = to-hex/size 1.2.3.4.5.6.7.8.9.10 20
 	--assert #0102030405           = to-hex/size 1.2.3.4.5.6.7.8.9.10 10
 
+--test-- {compose large block}
+	;@@ https://github.com/Oldes/Rebol-issues/issues/1906
+	b: copy [] insert/dup b 1 32768
+	--assert b = compose b ;- no crash
+
 ===end-group===
 
 ~~~end-file~~~