FIX: square-root -1 should return 1.#NaN instead of an error

fixes: Oldes/Rebol-issues#2431

Author: Oldes

src/core/n-math.c

@@ -391,7 +391,9 @@ enum {SINE, COSINE, TANGENT};
 ***********************************************************************/
 {
 	REBDEC dval = AS_DECIMAL(D_ARG(1));
+#ifdef USE_NO_INFINITY
 	if (dval < 0) Trap0(RE_POSITIVE);
+#endif
 	SET_DECIMAL(D_RET, sqrt(dval));
 	return R_RET;
 }

src/tests/units/decimal-test.r3

@@ -115,6 +115,16 @@ Rebol [
 		]
 ===end-group===
 
+
+===start-group=== "square-root"
+	--test-- "square-root 4"
+		--assert 2.0 = square-root 4
+	--test-- "square-root -1"
+	;@@ https://github.com/Oldes/Rebol-issues/issues/2431
+		--assert "1.#NaN" = mold try [square-root -1]
+===end-group===
+
+
 ===start-group=== "decimal issues"
 	--test-- "issue-1753"
 	;@@ https://github.com/Oldes/Rebol-issues/issues/1753