Adds test for empty contract w/ error recovery.

test/cmdlineTests/recovery_ast_empty_contract/args

@@ -0,0 +1 @@
+--error-recovery

test/cmdlineTests/recovery_ast_empty_contract/err

@@ -0,0 +1,8 @@
+Error: Expected pragma, import directive or contract/interface/library/struct/enum definition.
+ --> recovery_ast_empty_contract/input.sol:2:1:
+  |
+2 | c
+  | ^
+
+
+Compilation halted after AST generation due to errors.

test/cmdlineTests/recovery_ast_empty_contract/input.sol

@@ -0,0 +1,2 @@
+pragma 0.5.11;
+c