Don't auto outdent if preceding row is null

spec/app/edit-session-spec.coffee

@@ -2007,3 +2007,10 @@ describe "EditSession", ->
         expect(editSession.lineForBufferRow(2)).toBe "    0"
         expect(editSession.lineForBufferRow(3)).toBe "      2"
         expect(editSession.lineForBufferRow(4)).toBe "        4"
+
+  describe ".autoDecreaseIndentForRow()", ->
+      it "doesn't outdent the first and only row", ->
+        editSession.selectAll()
+        editSession.insertText("}")
+        editSession.autoDecreaseIndentForRow(0)
+        expect(editSession.lineForBufferRow(0)).toBe "}"

src/app/language-mode.coffee

@@ -189,6 +189,7 @@ class LanguageMode
 
     currentIndentLevel = @editSession.indentationForBufferRow(bufferRow)
     precedingRow = @buffer.previousNonBlankRow(bufferRow)
+    return unless precedingRow?
     precedingLine = @buffer.lineForRow(precedingRow)
 
     desiredIndentLevel = @editSession.indentationForBufferRow(precedingRow)