fix im2col in case of 2*2 input

src/operators/math/im2col.cpp

@@ -78,7 +78,7 @@ class Im2ColFunctor<ColFormat::kCFO, CPU, T> {
          (((isize - 2 * padding[0] + filter_height) % stride[0] == 0) ? 1 : 0));
     int fill = isize % 2;
     if (stride[0] == 1 && filter_height == 3 && pad1 && pad2 &&
-        dilation[0] == 1) {
+        dilation[0] == 1 && im_height > 2) {
       for (int c = 0; c < im_channels; ++c) {
         int oosize = osize * osize;
         int nk4 = osize / 4;
@@ -250,7 +250,7 @@ class Im2ColFunctor<ColFormat::kCFO, CPU, T> {
         im_data += isize * isize;
       }
     } else if (stride[0] == 2 && filter_height == 3 && pad1 &&
-               dilation[0] == 1) {
+               dilation[0] == 1 && im_height > 2) {
       for (int c = 0; c < im_channels; ++c) {
         int oosize = osize * osize;
         int nk4 = osize / 4;