Slider, Drags: skip %+ and %# format flags for scanning. (#6259)

(There are two additional unhandled flags that only affect padding: '-' and ' '. Formatting flags don't make sense in a SliderInt's format string, so I've omitted them)

docs/CHANGELOG.txt

@@ -44,6 +44,8 @@ Other changes:
   retaining underlying data. While we don't really want to encourage user not retaining
   underlying data, in the absence of a "late commit" behavior/flag we understand it may
   be desirable to take advantage of this trick. (#4714)
+- Drag, Sliders: Fixed parsing of text input when '+' or '#' format flags are used
+  in the format string. (#6259) [@idbrii]
 - Backends: OpenGL3: Fixed GL loader crash when GL_VERSION returns NULL. (#6154, #4445, #3530)
 - Backends: GLFW: Fixed key modifiers handling on secondary viewports. (#6248, #6034) [@aiekick]
 - Examples: Windows: Added 'misc/debuggers/imgui.natstepfilter' file to all Visual Studio projects,

imgui_widgets.cpp

@@ -3300,7 +3300,7 @@ void ImParseFormatSanitizeForPrinting(const char* fmt_in, char* fmt_out, size_t
     *fmt_out = 0; // Zero-terminate
 }
 
-// - For scanning we need to remove all width and precision fields "%3.7f" -> "%f". BUT don't strip types like "%I64d" which includes digits. ! "%07I64d" -> "%I64d"
+// - For scanning we need to remove all width and precision fields and flags "%+3.7f" -> "%f". BUT don't strip types like "%I64d" which includes digits. ! "%07I64d" -> "%I64d"
 const char* ImParseFormatSanitizeForScanning(const char* fmt_in, char* fmt_out, size_t fmt_out_size)
 {
     const char* fmt_end = ImParseFormatFindEnd(fmt_in);
@@ -3311,7 +3311,7 @@ const char* ImParseFormatSanitizeForScanning(const char* fmt_in, char* fmt_out,
     while (fmt_in < fmt_end)
     {
         char c = *fmt_in++;
-        if (!has_type && ((c >= '0' && c <= '9') || c == '.'))
+        if (!has_type && ((c >= '0' && c <= '9') || c == '.' || c == '+' || c == '#'))
             continue;
         has_type |= ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')); // Stop skipping digits
         if (c != '\'' && c != '$' && c != '_') // Custom flags provided by stb_sprintf.h. POSIX 2008 also supports '.