Fix library compilation errors

[amotl]

Dear Paul,

thanks a stack for conceiving this library. We are using it over at https://github.com/hiveeyes/arduino, and just discovered the corresponding firmwares won't build on recent PlatformIO environments ¹.

It's essentially about the issue @gibman reported at GH-3. This patch intends to fix it.

With kind regards,
Andreas.

Compiling .pio/build/nodemcu/lib9d8/TextFinder/TextFinder.cpp.o
.pio/libdeps/nodemcu/TextFinder/TextFinder.cpp: In member function 'float TextFinder::getFloat()':
.pio/libdeps/nodemcu/TextFinder/TextFinder.cpp:214:5: error: no return statement in function returning non-void [-Werror=return-type]
  214 |     }
      |     ^
.pio/libdeps/nodemcu/TextFinder/TextFinder.cpp: In member function 'float TextFinder::getFloat(char)':
.pio/libdeps/nodemcu/TextFinder/TextFinder.cpp:222:13: warning: unused variable 'fValue' [-Wunused-variable]
  222 |       float fValue;
      |             ^~~~~~
cc1plus: some warnings being treated as errors

Footnotes

1. https://github.com/hiveeyes/arduino/actions/runs/5062446319/jobs/9087977561#step:10:149 ↩