all: ignore parsing block image in paragraph

Previously, if we have block image in paragraph, we parse it as inline
image but with invalid src, for example

  image::my.png[multi
  line]

would be parsed as <img src=":imy.png" alt="multi line">.
This is incorrect according to asciidoctor output.

1 files changed, 7 insertions, 0 deletions

diff --git a/inline_parser.go b/inline_parser.go
index 621c21e..0e280d7 100644
--- a/inline_parser.go
+++ b/inline_parser.go
@@ -689,6 +689,13 @@ func parseInlineImage(doc *Document, content []byte) (elImage *element, n int) {
 		lineImage []byte
 	)
 
+	// If the next character is ':' (as in block "image::") mark it as
+	// invalid inline image, since this is block image that has been
+	// parsed but invalid (probably missing '[]').
+	if content[0] == ':' {
+		return nil, 0
+	}
+
 	_, n = indexByteUnescape(content, ']')
 	if n < 0 {
 		return nil, 0