Fixed a compilation error in double precision mode

platforms/opencl/src/kernels/findInteractingBlocks.cl

@@ -138,9 +138,9 @@ __kernel void findBlocksWithInteractions(real4 periodicBoxSize, real4 invPeriodi
 #ifdef USE_PERIODIC
                 blockDelta.xyz -= floor(blockDelta.xyz*invPeriodicBoxSize.xyz+0.5f)*periodicBoxSize.xyz;
 #endif
-                blockDelta.x = max(0.0f, fabs(blockDelta.x)-blockSizeX.x-blockSizeY.x);
-                blockDelta.y = max(0.0f, fabs(blockDelta.y)-blockSizeX.y-blockSizeY.y);
-                blockDelta.z = max(0.0f, fabs(blockDelta.z)-blockSizeX.z-blockSizeY.z);
+                blockDelta.x = max((real) 0, fabs(blockDelta.x)-blockSizeX.x-blockSizeY.x);
+                blockDelta.y = max((real) 0, fabs(blockDelta.y)-blockSizeX.y-blockSizeY.y);
+                blockDelta.z = max((real) 0, fabs(blockDelta.z)-blockSizeX.z-blockSizeY.z);
                 includeBlock2 &= (blockDelta.x*blockDelta.x+blockDelta.y*blockDelta.y+blockDelta.z*blockDelta.z < PADDED_CUTOFF_SQUARED);
                 if (includeBlock2) {
                     unsigned short y = (unsigned short) sortedBlocks[block2].y;