fix the B mass cut in the Bc builder
This MR fixes the too-low mass cut used in B meson combiners for B_c->Bmumu decays (StrippingB2OCMuMuBcLine), which removed all the signal.
StrippingReport INFO Event 35000, Good event 35000
| *Decision name*|*Rate,%*|*Accepted*| *Mult*|*ms/evt*|
|_StrippingGlobal_ | 0.6571| 230| | 28.903|
|_StrippingSequenceStreamLeptonic_ | 0.6571| 230| | 28.890|
|!StrippingB2OCMuMuLine | 0.3657| 128| 6.625| 26.715|
|!StrippingB2OCMuMuSSLine | 0.2029| 71| 2.535| 0.635|
|!StrippingB2OCMuMuBcLine | 0.0743| 26| 2.038| 0.093|
|!StrippingB2OCMuMuBcNoPointLine | 0.1600| 56| 1.893| 0.247|
|!StrippingB2OCMuMuLine_TIMING | 0.3657| 128| 6.625| 0.044|
|!StrippingB2OCMuMuSSLine_TIMING | 0.2029| 71| 2.535| 0.034|
|!StrippingB2OCMuMuBcLine_TIMING | 0.0743| 26| 2.038| 0.029|
|!StrippingB2OCMuMuBcNoPointLine_TIMING | 0.1600| 56| 1.893| 0.029|
as compared to the past MR !1480 (merged) (see the second table there), the rate increases only slightly for this affected line, while the others are unchanged, as expected.