fix enforcement of 1-step indentation

src/main.c

@@ -286,10 +286,13 @@ static int parse_indent(struct parser *p, int *indent, bool write) {
 		++i;
 	}
 	parser_pushch(p, ch);
-	if (ch == '\n' && *indent != 0) {
-		// Don't change indent when we encounter empty lines
+	if ((ch == '\n' || ch == UTF8_INVALID) && *indent != 0) {
+		// Don't change indent when we encounter empty lines or EOF
 		return *indent;
 	}
+	if (abs(i - *indent) > 1) {
+		parser_fatal(p, "Changed indentation by an amount greater than 1");
+	}
 	if (write) {
 		if (i < *indent) {
 			for (int j = *indent; i < j; --j) {
@@ -297,8 +300,6 @@ static int parse_indent(struct parser *p, int *indent, bool write) {
 			}
 		} else if (i == *indent + 1) {
 			fprintf(p->output, ".RS 4\n");
-		} else if (i != *indent && ch == '\t') {
-			parser_fatal(p, "Indented by an amount greater than 1");
 		}
 	}
 	*indent = i;

test/indent

@@ -19,3 +19,14 @@ Not indented
 Not indented
 EOF
 end 0
+
+begin "Disallows indentation changes > 1"
+scdoc <<EOF >/dev/null
+test(8)
+
+Not indented
+	Indented one level
+			Indented three levels
+Not indented
+EOF
+end 1