AP_GPS: fix blending when accuracy reported as 1mm

Thanks to Michael DuBreuil for suggesting the fix

libraries/AP_GPS/AP_GPS.cpp

@@ -1198,7 +1198,7 @@ bool AP_GPS::calc_blend_weights(void)
         // calculate the weights using the inverse of the variances
         float sum_of_hpos_weights = 0.0f;
         for (uint8_t i=0; i<GPS_MAX_RECEIVERS; i++) {
-            if (state[i].status >= GPS_OK_FIX_2D && state[i].horizontal_accuracy > 0.001f) {
+            if (state[i].status >= GPS_OK_FIX_2D && state[i].horizontal_accuracy >= 0.001f) {
                 hpos_blend_weights[i] = horizontal_accuracy_sum_sq / (state[i].horizontal_accuracy * state[i].horizontal_accuracy);
                 sum_of_hpos_weights += hpos_blend_weights[i];
             }
@@ -1218,7 +1218,7 @@ bool AP_GPS::calc_blend_weights(void)
         // calculate the weights using the inverse of the variances
         float sum_of_vpos_weights = 0.0f;
         for (uint8_t i=0; i<GPS_MAX_RECEIVERS; i++) {
-            if (state[i].status >= GPS_OK_FIX_3D && state[i].vertical_accuracy > 0.001f) {
+            if (state[i].status >= GPS_OK_FIX_3D && state[i].vertical_accuracy >= 0.001f) {
                 vpos_blend_weights[i] = vertical_accuracy_sum_sq / (state[i].vertical_accuracy * state[i].vertical_accuracy);
                 sum_of_vpos_weights += vpos_blend_weights[i];
             }
@@ -1238,7 +1238,7 @@ bool AP_GPS::calc_blend_weights(void)
         // calculate the weights using the inverse of the variances
         float sum_of_spd_weights = 0.0f;
         for (uint8_t i=0; i<GPS_MAX_RECEIVERS; i++) {
-            if (state[i].status >= GPS_OK_FIX_3D && state[i].speed_accuracy > 0.001f) {
+            if (state[i].status >= GPS_OK_FIX_3D && state[i].speed_accuracy >= 0.001f) {
                 spd_blend_weights[i] = speed_accuracy_sum_sq / (state[i].speed_accuracy * state[i].speed_accuracy);
                 sum_of_spd_weights += spd_blend_weights[i];
             }