Add unit test with bad write

If a partial write is made at the beginning,  the file was not being truncated.  Consequently writes would be accepted after it opens, and the those writes would be after the corruption so would never be read in the future.

src/leveled_cdb.erl

@@ -1266,6 +1266,8 @@ scan_over_file(Handle, Position, FilterFun, Output, LastKey) ->
     case saferead_keyvalue(Handle) of
         false ->
             leveled_log:log("CDB09", [Position]),
+            % Bring file back to that position
+            {ok, Position} = file:position(Handle, {bof, Position}),
             {eof, Output};
         {Key, ValueAsBin, KeyLength, ValueLength} ->
             NewPosition = case Key of
@@ -1315,7 +1317,7 @@ saferead_keyvalue(Handle) ->
     case read_next_2_integers(Handle) of 
         eof ->
             false;
-        {KeyL, ValueL} ->
+        {KeyL, ValueL} when is_integer(KeyL), is_integer(ValueL) ->
             case safe_read_next_keybin(Handle, KeyL) of 
                 false ->
                     false;
@@ -1327,7 +1329,9 @@ saferead_keyvalue(Handle) ->
                             % i.e. value with no CRC
                             {Key, TrueValue, KeyL, ValueL}
                     end
-            end
+            end;
+        _ ->
+            false
     end.
 
 
@@ -1434,7 +1438,7 @@ extract_valueandsize(ValueAsBin) ->
 %% Note that the endian_flip is required to make the file format compatible 
 %% with CDB 
 read_next_2_integers(Handle) ->
-    case file:read(Handle,?DWORD_SIZE) of 
+    case file:read(Handle, ?DWORD_SIZE) of 
         {ok, <<Int1:32,Int2:32>>} -> 
             {endian_flip(Int1), endian_flip(Int2)};
         ReadError ->
@@ -2565,6 +2569,20 @@ get_positions_corruption_test() ->
     ok = cdb_close(P3),
     file:delete(F2).
     
+badly_written_test() ->
+    F1 = "../test/badfirstwrite_test.pnd",
+    file:delete(F1),
+    {ok, Handle} = file:open(F1, ?WRITE_OPS),
+    ok = file:pwrite(Handle, 256 * ?DWORD_SIZE, <<1:8/integer>>),
+    ok = file:close(Handle),
+    {ok, P1} = cdb_open_writer(F1, #cdb_options{binary_mode=false}),
+    ok = cdb_put(P1, "Key100", "Value100"),
+    ?assertMatch({"Key100", "Value100"}, cdb_get(P1, "Key100")),
+    ok = cdb_close(P1),
+    {ok, P2} = cdb_open_writer(F1, #cdb_options{binary_mode=false}),
+    ?assertMatch({"Key100", "Value100"}, cdb_get(P2, "Key100")),
+    ok = cdb_close(P2),
+    file:delete(F1).
 
 
 nonsense_coverage_test() ->