fix gomarkdown#325?

parser/block.go

@@ -965,7 +965,12 @@ func (p *Parser) fencedCodeBlock(data []byte, doRender bool) int {
 
 		// did we reach the end of the buffer without a closing marker?
 		if end >= len(data) {
-			return 0
+			if doRender {
+				// process the rest of the data as part of the code block
+				work.Write(data[beg:])
+			}
+			beg = len(data)
+			break
 		}
 
 		// verbatim copy to the working buffer

parser/block_test.go

@@ -75,3 +75,12 @@ func TestRect(t *testing.T) {
 			input, exp, got)
 	}
 }
+
+func TestInfiniteLoopFix(t *testing.T) {
+	input := "```\n: "
+	p := NewWithExtensions(CommonExtensions)
+	doc := p.Parse([]byte(input))
+	if doc == nil {
+		t.Errorf("Expected non-nil AST")
+	}
+}