Static analyzers warnings

[ocornut]

Courtesy of PVS Studio:

implot_internal.h:532 | High | V730 | Not all members of a class (ImPlotTick) are initialized inside the constructor. Consider inspecting: PixelPos.
implot_internal.h:885 | High | V730 | Not all members of a class (ImPlotLegend) are initialized inside the constructor. Consider inspecting: PreviousLocation.
implot_internal.h:903 | High | V730 | Not all members of a class (ImPlotItemGroup) are initialized inside the constructor. Consider inspecting: ID.
implot_internal.h:860 | High | V730 | Not all members of a class (ImPlotItem) are initialized inside the constructor. Consider inspecting: Color.
implot_internal.h:1045 | High | V730 | Not all members of a class (ImPlotSubplot) are initialized inside the constructor. Consider inspecting: ID, Flags, PreviousFlags, TempSizes.

Not "fixing" because there might be an intent/good reason for those, otherwise easy to fix.

[ocornut]

Some more:

General Analysis	imgui_tests	implot.cpp:965	Medium	V1048	The 'Tm.tm_mon' variable was assigned the same value.
General Analysis	imgui_tests	implot.cpp:966	Medium	V1048	The 'Tm.tm_mday' variable was assigned the same value.
General Analysis	imgui_tests	implot.cpp:1149	Medium	V557	Array overrun is possible. The value of 'unit1' index could reach 8.
General Analysis	imgui_tests	implot.cpp:4905	Medium	V1004	The 'axis.OrthoAxis' pointer was used unsafely after it was verified against nullptr.
General Analysis	imgui_tests	implot.cpp:5276	Medium	V560	A part of conditional expression is always true: !clk.
General Analysis	imgui_tests	implot.cpp:964	Medium	V1048	The 'Tm.tm_year' variable was assigned the same value.
General Analysis	imgui_tests	implot_demo.cpp:95	Medium	V1044	Loop break conditions do not depend on the number of iterations.
General Analysis	imgui_tests	implot_demo.cpp:739	Medium	V601	The bool type is implicitly cast to the float type. Inspect the second argument.
General Analysis	imgui_tests	implot_demo.cpp:741	Medium	V601	The bool type is implicitly cast to the float type. Inspect the second argument.
General Analysis	imgui_tests	implot_internal.h:629	Medium	V730	Not all members of a class are initialized inside the constructor. Consider inspecting: ID, RangeCond, PixelMin, PixelMax, LinM, LogD, ...
General Analysis	imgui_tests	implot_internal.h:948	Medium	V730	It is possible that not all members of a class are initialized inside the constructor. Consider inspecting: ID.
General Analysis	imgui_tests	implot_internal.h:1096	Medium	V730	It is possible that not all members of a class are initialized inside the constructor. Consider inspecting: RenderLine, RenderFill, RenderMarkerLine, RenderMarkerFill, HiddenCond.
General Analysis	imgui_tests	implot_items.cpp:1044	Medium	V547	Expression 'marker != ImPlotMarker_None' is always true.
General Analysis	imgui_tests	implot_items.cpp:1617	Medium	V547	Expression 'marker != ImPlotMarker_None' is always true.

Sorry for the spam, I thought I'd submit because not everyone may have access to PVS Studio or static analyzers (although there's now one in Visual Studio) maybe there's a bug lurking behind one of one. Otherwise feel free to close :)

[epezent]

Thanks Omar! Very thoughtful of you to share these. Will defintely address these.