Fix T42800: Blender suddenly closes after pressing solve camera motion

Couple of issues:

- Fist/last frame calculation was wrong

- Keyframe selection might silently fail leading to unpredictable math
  errors all over the place. Now if keyframe selection fails solver wouldn't
  run.

extern/libmv/intern/reconstruction.cc

@@ -61,6 +61,7 @@ struct libmv_Reconstruction {
   CameraIntrinsics *intrinsics;
 
   double error;
+  bool is_valid;
 };
 
 namespace {
@@ -289,6 +290,12 @@ libmv_Reconstruction *libmv_solveReconstruction(
 
   LG << "number of markers for init: " << keyframe_markers.size();
 
+  if (keyframe_markers.size() < 8) {
+    LG << "No enough markers to initialize from";
+    libmv_reconstruction->is_valid = false;
+    return libmv_reconstruction;
+  }
+
   update_callback.invoke(0, "Initial reconstruction");
 
   EuclideanReconstructTwoFrames(keyframe_markers, &reconstruction);
@@ -319,6 +326,7 @@ libmv_Reconstruction *libmv_solveReconstruction(
                        progress_update_callback,
                        callback_customdata);
 
+  libmv_reconstruction->is_valid = true;
   return (libmv_Reconstruction *) libmv_reconstruction;
 }
 
@@ -377,9 +385,14 @@ libmv_Reconstruction *libmv_solveModal(
                        progress_update_callback,
                        callback_customdata);
 
+  libmv_reconstruction->is_valid = true;
   return (libmv_Reconstruction *) libmv_reconstruction;
 }
 
+int libmv_reconstructionIsValid(libmv_Reconstruction *libmv_reconstruction) {
+  return libmv_reconstruction->is_valid;
+}
+
 void libmv_reconstructionDestroy(libmv_Reconstruction *libmv_reconstruction) {
   LIBMV_OBJECT_DELETE(libmv_reconstruction->intrinsics, CameraIntrinsics);
   LIBMV_OBJECT_DELETE(libmv_reconstruction, libmv_Reconstruction);

extern/libmv/intern/reconstruction.h

@@ -68,6 +68,8 @@ libmv_Reconstruction* libmv_solveModal(
     reconstruct_progress_update_cb progress_update_callback,
     void* callback_customdata);
 
+int libmv_reconstructionIsValid(libmv_Reconstruction *libmv_reconstruction);
+
 void libmv_reconstructionDestroy(libmv_Reconstruction* libmv_reconstruction);
 
 int libmv_reprojectionPointForTrack(

extern/libmv/intern/stub.cc

@@ -138,6 +138,10 @@ libmv_Reconstruction *libmv_solveModal(
   return NULL;
 }
 
+int libmv_reconstructionIsValid(libmv_Reconstruction * /*libmv_reconstruction*/) {
+  return 0;
+}
+
 int libmv_reprojectionPointForTrack(
     const libmv_Reconstruction * /*libmv_reconstruction*/,
     int /*track*/,

source/blender/blenkernel/intern/tracking_solver.c

@@ -391,7 +391,7 @@ MovieReconstructContext *BKE_tracking_reconstruction_context_new(MovieClip *clip
 			last_marker--;
 		}
 
-		if (first < track->markersnr - 1)
+		if (first <= track->markersnr - 1)
 			sfra = min_ii(sfra, first_marker->framenr);
 
 		if (last >= 0)
@@ -509,6 +509,11 @@ bool BKE_tracking_reconstruction_finish(MovieReconstructContext *context, MovieT
 	MovieTrackingReconstruction *reconstruction;
 	MovieTrackingObject *object;
 
+	if (!libmv_reconstructionIsValid(context->reconstruction)) {
+		printf("Failed solve the motion: most likely there are no good keyframes\n");
+		return false;
+	}
+
 	tracks_map_merge(context->tracks_map, tracking);
 	BKE_tracking_dopesheet_tag_update(tracking);