Fix crash on decoding partial YAML

Sources/UniYAML/Decoder.swift

@@ -414,6 +414,9 @@ public struct UniYAML {
 				location = Range(uncheckedBounds: (index, border.lowerBound))
 				glue = (folded) ? " ":stream[border.lowerBound]
 			}
+			guard location.upperBound < stream.endIndex else {
+				break
+			}
 			index = stream.index(after: location.upperBound)
 			line += 1
 			if !value.isEmpty {

Tests/UniYAMLTests/UniYAMLTests.swift

@@ -34,6 +34,7 @@ class UniYAMLTests: XCTestCase {
 		("testYAMLUnexpectedEnd", testYAMLUnexpectedEnd),
 		("testPartialYAML", testPartialYAML),
 		("testPartialYAML2", testPartialYAML2),
+		("testPartialYAML3", testPartialYAML3),
 	]
 
 	let types = "---\n\nsimple string: a text\nquoted string: 'john ''beatle''\n lennon'\nsplit string: >\n  two\n  words\nrows: |\n  first\n  second\n  last\nint: -12345\nuint: 67890\ndouble: 3.14159265\npositive: yes\nnegative: off\n"
@@ -482,4 +483,18 @@ classic:
 		XCTAssert(obj == nil && err.hasPrefix("missing value at line 2"))
 	}
 
+	func testPartialYAML3() {
+		let yaml = "a: 3\n  b"
+		var obj: YAML?
+		var err: String = ""
+		do {
+			obj = try UniYAML.decode(yaml)
+		} catch UniYAMLError.error(let detail) {
+			err = detail
+		} catch {
+			print(error)
+		}
+		XCTAssert(obj == nil && err.hasPrefix("missing value at line 2"))
+	}
+
 }