Avoid infinite loop

Fixes: #11295

src/LyXAction.cpp

@@ -1517,7 +1517,7 @@ void LyXAction::init()
  * \li Params: outer:    If this is given, LyX will split the outermost environment in
                          the current nesting hierarchy.\n
                previous: If this is given, LyX will split the environment in the previous
-                         paragraph (is there is one).\n
+                         paragraph (if there is one).\n
                before:   If this is given, the new environment will be appended rather than
                          prepended.
  * \li Origin: spitz, 23 Dec 2012

src/Text3.cpp

@@ -1663,8 +1663,13 @@ void Text::dispatch(Cursor & cur, FuncRequest & cmd)
 			DocIterator scur = cur;
 			depth_type const max_depth = cur.paragraph().params().depth() + 1;
 			cur.forwardPar();
-			while (cur.paragraph().params().depth() < min(nextpar_depth, max_depth))
+			while (cur.paragraph().params().depth() < min(nextpar_depth, max_depth)) {
+				depth_type const olddepth = cur.paragraph().params().depth();
 				lyx::dispatch(FuncRequest(LFUN_DEPTH_INCREMENT));
+				if (olddepth == cur.paragraph().params().depth())
+					// leave loop if no incrementation happens
+					break;
+			}
 			cur.setCursor(scur);
 		}