The HSL equalizer line to show the color under the mouse pointer disappears when L*a*b* adjustments is On

[Sebastien Guyader]

To reproduce:

• turn HSL equalizer ON
• click on the button to add a control point: when you hover the mouse pointer on the preview, a line appears in the HSL equalizer panel to show the hue of the color under the mouse pointer
• turn L*a*b* Adjustments ON: now the line in the HSL equalizer disappears
• turn L*a*b* Adjustments OFF: the line in HSL panel is back

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[agriggio]

Lab adjustments: do not overwrite the pipette buffer of other tools earlier in the pipeline

Fixes #20

→ <<cset 14cbbcc32e13>>