Fix ExplicitLineBreak parsing

fuzzed index out of range and moved range check into for condition as \\
followed by spaces at the end of the inline text should not be turned into an
ExplicitLineBreak (just like \\ not followed by spaces).

org/inline.go

@@ -147,8 +147,8 @@ func (d *Document) parseExplicitLineBreakOrLatexFragment(input string, start int
 	switch {
 	case start+2 >= len(input):
 	case input[start+1] == '\\' && start != 0 && input[start-1] != '\n':
-		for i := start + 2; unicode.IsSpace(rune(input[i])); i++ {
-			if i >= len(input) || input[i] == '\n' {
+		for i := start + 2; i <= len(input)-1 && unicode.IsSpace(rune(input[i])); i++ {
+			if input[i] == '\n' {
 				return i + 1 - start, ExplicitLineBreak{}
 			}
 		}

org/testdata/misc.html

@@ -68,9 +68,11 @@
 </li>
 </ul>
 </li>
+<li><a href="#headline-30">index out of range in explicit line break parsing</a>
+</li>
 </ul>
 </li>
-<li><a href="#headline-30">Footnotes</a>
+<li><a href="#headline-31">Footnotes</a>
 </li>
 </ul>
 </nav>
@@ -499,7 +501,13 @@ <h3 id="headline-28">
 <h4 id="headline-29">
 [#B
 </h4>
-<h1 id="headline-30">
+<h3 id="headline-30">
+index out of range in explicit line break parsing
+</h3>
+<p>
+0\\ 
+</p>
+<h1 id="headline-31">
 Footnotes
 </h1>
 <div class="footnotes">

org/testdata/misc.org

@@ -136,6 +136,9 @@ When inserting an image link like [[/home/amos/Pictures/Screenshots/img-2017-09-
 ** misc fuzz / regression / edge case
 *** index out of range in headline priority parsing
 **** [#B
+*** index out of range in explicit line break parsing
+0\\ 
+
 * Footnotes
 
 [fn:1] a footnote /with/ *markup*

org/testdata/misc.pretty_org

@@ -136,6 +136,9 @@ When inserting an image link like [[/home/amos/Pictures/Screenshots/img-2017-09-
 ** misc fuzz / regression / edge case
 *** index out of range in headline priority parsing
 **** [#B
+*** index out of range in explicit line break parsing
+0\\ 
+
 * Footnotes
 
 [fn:1] a footnote /with/ *markup*